JP2011082503A - Substrate for power module, substrate for power module with heat sink, power module, and method of manufacturing substrate for power module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for power module that has metal plates and a ceramic substrate reliably joined together and is high in heat cycle reliability, and to provide a power module including the substrate for power module, and a method of manufacturing the substrate for power module. <P>SOLUTION: The substrate 10 for power module has the metal plates 12 and 13, made of aluminum, stacked and joined on surfaces of the ceramic substrate 11, wherein one or more additional elements selected out of Zn, Ge, Ag, Mg, Ca, Ga, and Li are solid-dissolved in the metal plates 12 and 13 in addition to Cu, and a total of Cu concentrations and concentrations of the additional elements near interfaces of the metal plates 12 and 13 with the ceramic substrate 11 is set to be 0.05 to 5 mass%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power module substrate used in a semiconductor device for controlling a large current and a high voltage, a power module substrate with a heat sink, a power module including the power module substrate, and a method for manufacturing the power module substrate. It is.

Among semiconductor elements, a power element for supplying power has a relatively high calorific value. Therefore, as a substrate on which the power element is mounted, for example, as shown in Patent Document 1, an Al (AlN (aluminum nitride)) ceramic substrate is made of Al ( A power module substrate in which a metal plate of (aluminum) is bonded via a brazing material is used.
The metal plate is formed as a circuit layer, and a power element (semiconductor element) 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.

  As a means for forming a circuit layer, in addition to a method of forming a circuit pattern on a metal plate after bonding the metal plate to a ceramic substrate, for example, as disclosed in Patent Document 2, a circuit pattern is previously provided. There has been proposed a method of joining a metal piece formed in a shape to a ceramic substrate.

  Here, 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 3 discloses a technique in which the surface roughness of the ceramic substrate is less than 0.5 μm. Has been.

JP 2003-086744 A JP 2008-311294 A 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.

  In particular, power modules have recently been reduced in size and thickness, and the usage environment has become stricter, and the amount of heat generated from electronic components such as mounted semiconductor elements tends to increase. Thus, it is necessary to dispose the power module substrate on the heat sink. 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 loading. There is a demand for improvement in bonding strength and reliability between the metal plate and the metal plate.

  The present invention has been made in view of the above-described circumstances, in which a metal plate and a ceramic substrate are securely bonded to each other, a power module substrate having a high heat cycle reliability, a power module substrate with a heat sink, and the power module. It is an object of the present invention to provide a power module including a power board and a method for manufacturing the power module board.

  In order to solve such problems and achieve the above object, the power module substrate of the present invention is a power module substrate in which a metal plate made of aluminum is laminated and bonded to the surface of a ceramic substrate. In addition to Cu, the metal plate contains one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li in solid solution. Among these, the total of the Cu concentration in the vicinity of the interface with the ceramic substrate and the concentration of the additive element is set in a range of 0.05 mass% or more and 5 mass% or less.

In the power module substrate having this structure, in addition to Cu, one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga and Li are dissolved in the metal plate. Therefore, the bonding interface side portion of the metal plate is strengthened by solid solution. Thereby, the fracture | rupture in a metal plate part can be prevented and joining reliability can be improved.
Here, since the total concentration of Cu and the additive element in the vicinity of the interface with the ceramic substrate in the metal plate is 0.05% by mass or more, it is possible to reliably dissolve the bonding interface side portion of the metal plate. Can be strengthened. In addition, since the total concentration of Cu and the additive element in the vicinity of the interface with the ceramic substrate of the metal plate is 5% by mass or less, the strength of the bonding interface of the metal plate is prevented from becoming excessively high. When the cooling cycle is applied to the power module substrate, the thermal stress can be absorbed by the metal plate, and cracking of the ceramic substrate can be prevented.

The width of the ceramic substrate is set wider than the width of the metal plate, and a structure in which a Cu precipitation portion in which a compound containing Cu is precipitated in aluminum is formed at the width direction end portion of the metal plate is adopted. It is preferable.
In this case, since the Cu precipitation portion is formed at the end portion in the width direction of the metal plate, the end portion in the width direction of the metal plate can be strengthened by precipitation. Thereby, generation | occurrence | production of the fracture | rupture from the width direction edge part of a metal plate can be prevented, and joining reliability can be improved.

Here, the ceramic substrate is made of AlN or Si ₃ N ₄ , and the oxygen concentration at the bonding interface between the metal plate and the ceramic substrate is higher than the oxygen concentration in the metal plate and the ceramic substrate. The oxygen high concentration portion may be formed, and the thickness of the oxygen high concentration portion may be 4 nm or less.
In this case, an oxygen high concentration portion in which the oxygen concentration is higher than the oxygen concentration in the metal plate and the ceramic substrate is formed at the bonding interface between the ceramic substrate made of AlN or Si ₃ N ₄ and the metal plate made of aluminum. Since it is formed, the bonding strength between the ceramic substrate made of AlN or Si ₃ N ₄ and the metal plate made of aluminum is improved by oxygen present at the bonding interface. Furthermore, since the thickness of the high oxygen concentration portion is 4 nm or less, the occurrence of cracks in the high oxygen concentration portion due to stress when a thermal cycle is applied is suppressed.
Here, the oxygen concentration in the metal plate and the ceramic substrate is an oxygen concentration in a portion of the metal plate and the ceramic substrate that is away from the bonding interface by a certain distance (for example, 50 nm or more).

A power module substrate with a heat sink according to the present invention includes the above-described power module substrate and a heat sink that cools the power module substrate.
According to the power module substrate with a heat sink having this structure, since the heat module for cooling the power module substrate is provided, the heat generated in the power module substrate can be efficiently cooled by the heat sink.

A power module according to the present invention includes the power module substrate described above 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 method for manufacturing a power module substrate of the present invention is a method for manufacturing a power module substrate in which a metal plate made of aluminum is laminated and bonded to the surface of a ceramic substrate, the bonding surface of the ceramic substrate and the metal In addition to Cu, one or more additional elements selected from Zn, Ge, Ag, Mg, Ca, Ga and Li are fixed to at least one of the joining surfaces of the plates, and Cu and the additional elements are fixed. A fixing step of forming a fixing layer containing, a stacking step of stacking the ceramic substrate and the metal plate via the fixing layer, and pressing the stacked ceramic substrate and the metal plate in the stacking direction By heating and forming a molten metal region at the interface between the ceramic substrate and the metal plate, and solidifying the molten metal region Anda solidification step of bonding the metal plate and the ceramic substrate, in the fixing step, the interface between the ceramic substrate and the metal plate, Cu and the additive element, 0.1 mg / cm ² or more 10 mg / cm ² or less, and in the heating step, by diffusing Cu and the additive element of the fixing layer to the metal plate side, the interface between the ceramic substrate and the metal plate, It is characterized by forming a molten metal region.

According to the method for manufacturing a power module substrate having this configuration, at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate is added to Cu, Zn, Ge, Ag, Mg, Ca, Ga, and Since there is a fixing step of fixing one or more additional elements selected from Li and forming a fixing layer containing Cu and the additional elements, the bonding interface between the metal plate and the ceramic substrate is provided. In addition to Cu, one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li are present. Here, elements such as Cu and Zn, Ge, Ag, Mg, Ca, Ga, and Li are elements that lower the melting point of aluminum, and therefore, at the interface between the metal plate and the ceramic substrate at a relatively low temperature condition. A molten metal region can be formed. In addition, since Cu is an element highly reactive with Al, the presence of Cu in the vicinity of the bonding interface activates the surface of the metal plate made of aluminum.
Therefore, it is possible to firmly bond the ceramic substrate and the metal plate even if they are bonded under relatively low temperature and short time bonding conditions.

  Further, in the heating step, the molten metal region is formed at the interface between the ceramic substrate and the metal plate by diffusing Cu of the fixing layer and the additive element toward the metal plate, and the molten metal region is Since it is configured to join the metal plate and the ceramic substrate by solidifying, it is not necessary to use a brazing material foil or the like, and the power module substrate in which the metal plate and the ceramic substrate are securely joined at low cost. Can be manufactured.

  Thus, since the ceramic substrate and the metal plate can be joined without using a brazing material foil, it is not necessary to perform an alignment operation or the like of the brazing material foil. Even when the formed metal piece is bonded to the ceramic substrate, troubles due to misalignment can be prevented in advance.

Further, in the fixing step, the amount of Cu and the additional element fixed at the interface between the ceramic substrate and the metal plate is 0.1 mg / cm ² or more, so that the interface between the ceramic substrate and the metal plate is The molten metal region can be reliably formed, and the ceramic substrate and the metal plate can be firmly bonded.
Furthermore, since the fixed amount of Cu and the additional element interposed at the interface between the ceramic substrate and the metal plate is 10 mg / cm ² or less, it is possible to prevent the generation of cracks in the fixed layer, A molten metal region can be reliably formed at the interface between the substrate and the metal plate. Furthermore, it is possible to prevent Cu and the additive element from excessively diffusing to the metal plate side and excessively increasing the strength of the metal plate near the interface. Therefore, when a cooling cycle is loaded on the power module substrate, the thermal stress can be absorbed by the metal plate, and cracking of the ceramic substrate can be prevented.

Furthermore, in the fixing step, Cu and the additive element are interposed in the interface between the ceramic substrate and the metal plate within a range of 0.1 mg / cm ² or more and 10 mg / cm ² or less. It is possible to manufacture a power module substrate in which the total concentration of Cu and the additive element in the vicinity of the interface with the ceramic substrate in the plate is in the range of 0.05% by mass to 3% by mass.

  Moreover, since the fixing layer is formed directly on the metal plate and the ceramic substrate, the oxide film is formed only on the surface of the metal plate, and the total thickness of the oxide film existing at the interface between the metal plate and the ceramic substrate. Therefore, the yield of initial bonding is improved.

  In addition, although it is set as the structure which adheres Cu and the said additional element directly to at least one among the joining surface of the said ceramic substrate and the joining surface of the said metal plate, from a viewpoint of productivity, Cu and the said addition are added to the joining surface of a metal plate. It is preferable to fix the elements. When Cu and the additive element are fixed to the bonding surface of the ceramic substrate, Cu and the additive element must be fixed to each ceramic substrate. On the other hand, when Cu and the additive element are fixed to the joint surface of the metal plate, Cu and the continuous metal strip are continuously formed from one end to the other end of the long metal strip wound in a roll shape. It is possible to fix the additive element, and the productivity is excellent.

  In addition, Cu and the additive element may be fixed to at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate, respectively, to form the Cu layer and the additive element layer. Alternatively, Cu and the additional element may be simultaneously fixed to at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate to form a fixed layer of Cu and the additional element.

Here, in the fixing step, it is preferable that Al is fixed together with Cu and the additive element.
In this case, since Al is fixed together with Cu and the additive element, the formed fixed layer contains Al, and in the heating process, the fixed layer is preferentially melted to ensure the molten metal region. Thus, the ceramic substrate and the metal plate can be firmly bonded. Moreover, oxidation of oxidation active elements, such as Mg, Ca, Li, can be prevented. In order to fix Al together with Cu and the additive element, Cu and the additive element and Al may be vapor-deposited simultaneously, or sputtering may be performed using an alloy of Cu, the additive element and Al as a target. Furthermore, Cu and additive elements and Al may be laminated.

Further, the fixing step may include at least one of a bonding surface of the ceramic substrate and a bonding surface of the metal plate by plating, vapor deposition, CVD, sputtering, cold spray, or application of paste and ink in which powder is dispersed. On the other hand, it is preferable to fix Cu and one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga and Li.
In this case, Cu and the additive element are applied to the bonding surface of the ceramic substrate and the bonding surface of the metal plate by plating, vapor deposition, CVD, sputtering, cold spray, or application of paste and ink in which powder is dispersed. Since it is securely fixed to at least one of them, it becomes possible to reliably interpose Cu and the additive element at the bonding interface between the ceramic substrate and the metal plate. In addition, it is possible to accurately adjust the amount of Cu and the additive element to be fixed, and it is possible to securely form the molten metal region and firmly bond the ceramic substrate and the metal plate.

  According to the present invention, a metal plate and a ceramic substrate are securely bonded to each other, and a power module substrate having a high heat cycle reliability, a power module substrate with a heat sink, a power module including the power module substrate, and the power module It is possible to provide a method for manufacturing a manufacturing substrate.

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 Cu density | concentration and additive element density | concentration of the circuit layer and metal layer of the board | substrate for power modules which are 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 a flowchart 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 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 and ceramic substrate in FIG. It is a flowchart which shows the manufacturing method of the board | substrate for power modules which is other embodiment of this invention. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules which is other embodiment of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a power module substrate, a power module substrate with a heat sink, and a power module according to an 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 highly insulating AlN (aluminum nitride). 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. In the present embodiment, as shown in FIG. 1, the width of the ceramic substrate 11 (the length in the left-right direction in FIG. 1) is set wider than the width of the circuit layer 12 and the metal layer 13.

  As shown in FIG. 5, 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.

  As shown in FIG. 5, 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 the top plate portion 5 joined to the power module substrate 10 and the flow path 6 for circulating a cooling medium (for example, cooling water). And. 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. .

As shown in FIG. 2, the circuit layer 12 (metal plate 22) is formed at the center in the width direction of the bonding interface 30 between the ceramic substrate 11, the circuit layer 12 (metal plate 22), and the metal layer 13 (metal plate 23). ) And the metal layer 13 (metal plate 23), in addition to Cu, one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga and Li are in solid solution. In the vicinity of the bonding interface 30 between the circuit layer 12 and the metal layer 13, a concentration gradient layer 33 is formed in which the Cu concentration and the concentration of the additive element gradually decrease as the distance from the bonding interface 30 in the stacking direction increases. Here, the total concentration of Cu and the additive element on the bonding interface 30 side of the concentration gradient layer 33 (in the vicinity of the bonding interface 30 between the circuit layer 12 and the metal layer 13) is 0.05% by mass or more and 5% by mass or less. It is set within the range.
Note that the concentrations of Cu and the additive element in the vicinity of the bonding interface 30 between the circuit layer 12 and the metal layer 13 are average values measured at five points from the bonding interface 30 by EPMA analysis (spot diameter of 30 μm). The graph of FIG. 2 is obtained by performing line analysis in the stacking direction in the central portion of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23), and obtaining the above-mentioned concentration at the 50 μm position as a reference. It is.

  Here, in this embodiment, Ge is used as an additive element, the Ge concentration in the vicinity of the bonding interface 30 between the circuit layer 12 and the metal layer 13 is 0.05 mass% or more and 1 mass% or less, and the Cu concentration is 0.05. It is set within the range of 1% by mass or more.

Further, at the end portion in the width direction of 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), a Cu-containing compound is precipitated in the aluminum matrix. A precipitation portion 35 is formed. Here, Cu concentration in this Cu precipitation part 35 is set in the range of 0.5 mass% or more and 5.0 mass% or less, and Cu exceeding the amount of solid solution in aluminum is contained. .
Note that the Cu concentration of the Cu precipitation portion 35 is an average value measured at five points by EPMA analysis (spot diameter of 30 μm).

Further, 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. An oxygen high concentration portion 32 in which oxygen is concentrated is formed. In the oxygen high concentration portion 32, the oxygen concentration is higher than the oxygen concentration in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23). Note that the thickness H of the oxygen high concentration portion 32 is 4 nm or less.
Note that, as shown in FIG. 3, the bonding interface 30 observed here is a lattice image of the circuit board 12 (metal plate 22) and the metal layer 13 (metal plate 23) on the interface side and the ceramic substrate 11. The reference plane S is the center between the end of the bonding interface side.

  Below, the manufacturing method of the board | substrate 10 for power modules of the above-mentioned structure is demonstrated with reference to FIGS.

(Fixing step S1)
First, as shown in FIGS. 5 and 6, one type selected from Cu and Zn, Ge, Ag, Mg, Ca, Ga, and Li is formed on the respective joint surfaces of the metal plates 22 and 23 by sputtering. Two or more additional elements are fixed to form the fixed layers 24 and 25.
Here, in this embodiment, Ge is used as an additive element, the Cu amount in the fixed layers 24 and 25 is 0.08 mg / cm ² or more and 2.7 mg / cm ² or less, and the Ge amount is 0.002 mg / cm ^2. It is set to 2.5 mg / cm ² or less.

(Lamination process S2)
Next, as shown in FIG. 5, the metal plate 22 is laminated on one surface side of the ceramic substrate 11, and the metal plate 23 is laminated on the other surface side of the ceramic substrate 11. At this time, as shown in FIGS. 5 and 6, the metal plates 22 and 23 are laminated so that the surfaces on which the fixing layers 24 and 25 are formed face the ceramic substrate 11. That is, the fixing layers 24 and 25 (Cu and the additive element) are interposed between the metal plates 22 and 23 and the ceramic substrate 11, respectively. In this way, the laminate 20 is formed.

(Heating step S3)
Next, the stacked body 20 formed in the stacking step S2 is charged in a stacking direction (pressure 1 to 35 kgf / cm ² ) in a vacuum heating furnace and heated, as shown in FIG. In addition, molten metal regions 26 and 27 are formed at the interfaces between the metal plates 22 and 23 and the ceramic substrate 11, respectively. As shown in FIG. 6, the molten metal regions 26 and 27 are formed in the fixed layers 24 and 25 of the metal plates 22 and 23 by diffusing the Cu and the additive element to the metal plates 22 and 23 side. It is formed by increasing the Cu concentration in the vicinity of 25 and the concentration of the additive element (Ge concentration in this embodiment) and lowering the melting point. When the pressure is less than 1 kgf / cm ² , there is a possibility that the ceramic substrate 11 and the metal plates 22 and 23 cannot be bonded well. Moreover, when the above-mentioned pressure exceeds 35 kgf / cm < ² >, there exists a possibility that the metal plates 22 and 23 may deform | transform. Therefore, the above-mentioned pressurizing pressure is preferably in the range of 1 to 35 kgf / cm ² .
Here, in this embodiment, the pressure in the vacuum heating furnace is set in a range of 10 ⁻⁶ to 10 ⁻³ Pa, and the heating temperature is set in a range of 550 ° C. or more and 650 ° C. or less.

(Coagulation step S4)
Next, the temperature is kept constant with the molten metal regions 26 and 27 formed. Then, Cu and the additive element (Ge in this embodiment) in the molten metal regions 26 and 27 are further diffused toward the metal plates 22 and 23. As a result, the Cu concentration and the concentration of the additive element (Ge concentration in the present embodiment) in the portions that were the molten metal regions 26 and 27 are gradually decreased, and the melting point is increased, and the temperature is kept constant. Solidification will proceed in the held state. That is, the ceramic substrate 11 and the metal plates 22 and 23 are joined by so-called diffusion bonding (Transient Liquid Phase Diffusion Bonding). After solidification progresses in this way, cooling is performed to room temperature.

  In this way, the metal plates 22 and 23 to be the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 are joined, and the power module substrate 10 according to the present embodiment is manufactured.

  In the power module substrate 10 and the power module 1 according to the present embodiment configured as described above, Cu and the additive element (Ge in the present embodiment) are fixed to the joint surfaces of the metal plates 22 and 23. Since the fixing step S <b> 1 is provided, Cu and the additive element are present in the bonding interface 30 between the metal plates 22 and 23 and the ceramic substrate 11. Here, since Cu is an element highly reactive with Al, the presence of Cu at the bonding interface 30 activates the surfaces of the metal plates 22 and 23 made of aluminum. Therefore, the ceramic substrate 11 and the metal plates 22 and 23 can be firmly bonded.

  Furthermore, the ceramic substrate 11, the circuit layer 12 (metal plate 22), and the metal layer 13 (metal plate 23) are formed on the bonding surfaces of the metal plates 22 and 23, and the fixing layer 24 containing Cu and the additive element, 25 Cu and the additive element are diffused toward the metal plates 22 and 23 to form the molten metal regions 26 and 27, and the Cu and the additive element in the molten metal regions 26 and 27 are transferred to the metal plates 22 and 23. Since it is solidified and bonded by diffusion, the ceramic substrate 11 and the metal plates 22 and 23 can be firmly bonded even when bonded under relatively low temperature and short time bonding conditions. In particular, Cu, and elements such as Zn, Ge, Ag, Mg, Ca, Ga, and Li lower the melting point of aluminum, so that bonding under low temperature conditions is possible.

Further, at the center portion in the width direction of 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), the circuit layer 12 (metal plate 22) and the metal layer 13 (metal) Cu and the additive element are dissolved in the plate 23), and the total concentration of Cu and the additive element on the bonding interface 30 side of the circuit layer 12 and the metal layer 13 is 0.05% by mass or more and 5% by mass. In the present embodiment, Ge is used as an additive element, and the Ge concentration in the vicinity of the junction interface 30 between the circuit layer 12 and the metal layer 13 is 0.05 mass% or more and 1 mass%. Hereinafter, since the Cu concentration is set in the range of 0.05% by mass or more and 1% by mass or less, the portion of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) on the bonding interface 30 side is Solid solution strengthened, circuit layer 12 (metal plate It is possible to prevent the occurrence of cracks in 2) and the metal layer 13 (metal plate 23).
Further, in the heating step S3, Cu and the additive element are sufficiently diffused to the metal plates 22 and 23 side, and the metal plates 22 and 23 and the ceramic substrate 11 are firmly bonded.

  Further, in the present embodiment, the ceramic substrate 11 is made of AlN, and the oxygen concentration is present at the bonding interface 30 between the metal plates 22 and 23 to be the circuit layer 12 and the metal layer 13 and the ceramic substrate 11. Since the oxygen high concentration part 32 made higher than the oxygen concentration in the metal plates 22 and 23 constituting the metal layer 13 is generated, the bonding strength between the ceramic substrate 11 and the metal plates 22 and 23 is improved by this oxygen. Can be achieved. Moreover, since the thickness of the high oxygen concentration portion 32 is 4 nm or less, the occurrence of cracks in the high oxygen concentration portion 32 due to the stress when a thermal cycle is loaded is suppressed.

  In addition, a fixing step S1 is provided to fix the Cu and the additional element to the bonding surface of the metal plate to form the fixing layers 24 and 25. In the heating step S3, Cu and the additional element of the fixing layers 24 and 25 are added. Since the molten metal regions 26 and 27 are formed at the interface between the ceramic substrate 11 and the metal plates 22 and 23 by diffusing to the metal plates 22 and 23 side, it is necessary to use a brazing material foil that is difficult to manufacture. Thus, the power module substrate 10 in which the metal plates 22 and 23 and the ceramic substrate 11 are reliably bonded can be manufactured at low cost.

In the present embodiment, in the fixing step S1, the amount of Cu and the amount of Ge interposed at the interface between the ceramic substrate 11 and the metal plates 22 and 23 are set to Cu: 0.08 mg / cm ² or more, Ge: 0.002 mg. / Cm ² or more, the molten metal regions 26 and 27 can be reliably formed at the interface between the ceramic substrate 11 and the metal plates 22 and 23, and the ceramic substrate 11 and the metal plates 22 and 23 are firmly formed. It becomes possible to join.

Furthermore, since the Cu amount and Ge amount interposed at the interface between the ceramic substrate 11 and the metal plates 22 and 23 are Cu: 2.7 mg / cm ² or less and Ge: 2.5 mg / cm ² or less, the fixing layer It is possible to prevent cracks 24 and 25 from being generated, and the molten metal regions 26 and 27 can be reliably formed at the interface between the ceramic substrate 11 and the metal plates 22 and 23. Furthermore, it is possible to prevent Cu and the additive element from excessively diffusing to the metal plates 22 and 23 side and excessively increasing the strength of the metal plates 22 and 23 in the vicinity of the interface. Therefore, when the cooling cycle is applied to the power module substrate 10, the thermal stress can be absorbed by the circuit layer 12 and the metal layer 13 (metal plates 22 and 23), and cracking of the ceramic substrate 11 can be prevented. .

Further, since the fixing layers 24 and 25 are formed directly on the joint surfaces of the metal plates 22 and 23 without using the brazing material foil, it is not necessary to perform the alignment work of the brazing material foil, and the ceramics can be surely used. The board | substrate 11 and the metal plates 22 and 23 can be joined. Therefore, this power module substrate 10 can be produced efficiently.
In addition, since the fixing layers 24 and 25 are formed on the joining surfaces of the metal plates 22 and 23, the oxide film interposed at the interface between the metal plates 22 and 23 and the ceramic substrate 11 is formed on the surfaces of the metal plates 22 and 23. Therefore, the yield of initial bonding can be improved.

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.

Further, in the fixing process, it has been described that the Cu and the additive element are fixed to the bonding surface of the metal plate. However, the present invention is not limited to this, and Cu and the additive element are added to the bonding surface of the ceramic substrate. Cu and the additive element may be fixed to the bonding surface of the ceramic substrate and the bonding surface of the metal plate, respectively.
Furthermore, in the fixing step, it has been described that Cu and the additional element are fixed by sputtering, but the present invention is not limited to this, and plating, vapor deposition, CVD, cold spray, or a paste in which powder is dispersed and Cu and the additive element may be fixed by application of ink or the like.

  Moreover, although Cu and the said additional element were fixed, it demonstrated as what forms the fixed layer containing Cu and the said additional element, but it is not limited to this, As shown in FIG.7 and FIG.8. Cu layers 124A and 125A and additive element layers 124B and 125B may be formed on at least one of the bonding surface of the ceramic substrate 111 or the bonding surfaces of the metal plates 123 and 124, respectively. That is, the fixing step S1 may be separated into the Cu fixing step S10 and the additive element fixing step S11. Further, a Cu fixing step may be provided after the additive element fixing step.

Further, an alloy layer of Cu and an additive element may be formed using an alloy of the additive element and Cu.
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 an aluminum alloy or a composite material containing aluminum. Furthermore, although the description has been made with the heat sink having the flow path of the cooling medium, the structure of the heat sink is not particularly limited, and heat sinks having various configurations can be used.

Further, the ceramic substrate has been described as being composed of AlN, it is not limited _{thereto, Si 3 N 4, Al 2} O 3 may be constituted by other ceramics such.

A comparative experiment conducted to confirm the effectiveness of the present invention will be described.
A power module substrate is fabricated by bonding a circuit layer made of 4N aluminum having a thickness of 0.6 mm and a metal layer made of 4N aluminum having a thickness of 0.6 mm to a ceramic substrate made of AlN having a thickness of 0.635 mm. did.
Here, on the joint surface of the aluminum plate (4N aluminum) to be the circuit layer and the metal layer, Cu and an additive element are fixed to form a fixed layer, the metal plate and the ceramic substrate are laminated, and heated under pressure, A metal plate and a ceramic substrate were joined.

And various test pieces which changed the adhering additive element were produced, and joining reliability was evaluated using these test pieces. As an evaluation of the bonding reliability, the bonding rates after 2000 times of the thermal cycle (−45 ° C.-125 ° C.) were compared. The results are shown in Tables 1 to 3.
In addition, the joining rate was computed with the following formula | equation. Here, the initial bonding area is an area to be bonded before bonding.
Bonding rate = (initial bonding area-peeling area) / initial bonding area

  Moreover, about these test pieces, the density | concentration of Cu and the addition element of the joining vicinity of a ceramic substrate among metal plates (50 micrometers from a joining interface) was measured by EPMA analysis (spot diameter of 30 micrometers). The total concentration of Cu and additive elements is also shown in Table 1-3.

The amount of Cu in the fixed layer is 0.01 mg / cm ² (thickness conversion 0.011 μm), and the amount of the additional element (Li) fixed is 0.05 mg / cm ² (thickness conversion 0.935 μm). In Comparative Example 1 in which the total of 0.06 mg / cm ² was obtained, the joining rate after 2000 times of the cooling and heating cycle (−45 ° C. to 125 ° C.) was 49.2%, which was a very low value. This is considered to be because the amount of Cu and the amount of additive element (Li) present at the interface were small, and the molten metal region could not be sufficiently formed at the interface between the metal plate and the ceramic substrate.

The amount of Cu in the fixing layer is 2.4 mg / cm ² (thickness conversion: 2.69 μm), the amount of fixing of the additive element (Ge) is 2.4 mg / cm ² (thickness conversion: 4.51 μm), and the additional element (Ag amount sticking) is a 5.3 mg / cm ² (thickness in terms 5.05Myuemu), total fixation quantity in Comparative example 2 was set to 10.1 mg / cm ^2, thermal cycle (-45 ° C. -125 ° C. ) Was repeated 2000 times, and the bonding rate was 63.3%. This is presumably because the amount of Cu and additive elements (Ge, Ag) is so large that the metal plate becomes too hard, and thermal stress due to the thermal cycle is applied to the joint interface.

On the other hand, in this invention example 1-63, all the joining rates after repeating a cooling-heat cycle (-45 degreeC-125 degreeC) 2000 times were 93% or more.
In addition, the amount of Cu in the fixing layer is 0.01 mg / cm ² (thickness conversion 0.011 μm), and the amount of fixing of the additive element (Li) is 0.09 mg / cm ² (thickness conversion 1.68 μm), Invention Example 64 in which the total amount of fixing was 0.1 mg / cm ² and the amount of Cu in the fixing layer was 2.4 mg / cm ² (thickness conversion 2.69 μm), and the amount of fixing of the additive element (Ge) was 2.1 mg / cm ² (thickness conversion: 3.95 μm), the additive element (Ag) sticking amount is 5.1 mg / cm ² (thickness conversion: 4.86 μm), and the total sticking amount is 9.6 mg / cm ^2. Also in Example 65 of the present invention, which was set to cm ² , the bonding rate after 2000 times of the cooling / heating cycle (−45 ° C. to 125 ° C.) exceeded 70%.
From this result, according to the example of the present invention, it is possible to reliably form a molten metal region at the interface between the metal plate and the ceramic substrate by the diffusion of Cu and various additive elements, and the metal plate and the ceramic substrate are firmly bonded. It is judged that it was able to be joined.

  In Inventive Example 1-65, the total concentration of Cu and various additive elements in the vicinity of the bonding interface of the ceramic substrate (50 μm from the bonding interface) in the metal plate is in the range of 0.05 mass% or more and 5 mass% or less. It was confirmed that

1 Power module 3 Semiconductor chip (electronic component)
10 Power module substrate 11, 111 Ceramic substrate 12, 112 Circuit layer 13, 113 Metal layer 22, 23, 122, 123 Metal plate 24, 25 Adhering layer 26, 27, 126, 127 Molten metal region 30, 130 Bonding interface 124A 125A Cu layer 124B, 125B Additive element layer

Claims (8)

A power module substrate in which a metal plate made of aluminum is laminated and bonded to the surface of a ceramic substrate,
In the metal plate, in addition to Cu, one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li are solid-dissolved. A power module substrate, characterized in that the sum of the Cu concentration in the vicinity of the interface with the ceramic substrate and the concentration of the additive element is set in a range of 0.05 mass% or more and 5 mass% or less.   The width of the ceramic substrate is set wider than the width of the metal plate, and a Cu precipitation portion in which a compound containing Cu is precipitated in aluminum is formed at the width direction end portion of the metal plate. The power module substrate according to claim 1. The ceramic substrate is made of AlN or Si ₃ N ₄ , and the oxygen concentration is higher than the oxygen concentration in the metal plate and the ceramic substrate at the bonding interface between the metal plate and the ceramic substrate. The power module substrate according to claim 1, wherein a high concentration portion is formed, and the thickness of the oxygen high concentration portion is 4 nm or less.   A power module substrate with a heat sink, comprising: the power module substrate according to any one of claims 1 to 3; and a heat sink that cools the power module substrate.   A power module comprising: the power module substrate according to any one of claims 1 to 3; and an electronic component mounted on the power module substrate. A method for manufacturing a power module substrate in which a metal plate made of aluminum is laminated and bonded to the surface of a ceramic substrate,
In addition to Cu, at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate is one or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga, and Li. Fixing step, forming a fixing layer containing Cu and the additive element,
A laminating step of laminating the ceramic substrate and the metal plate via the fixing layer;
Heating and pressurizing and heating the laminated ceramic substrate and the metal plate in a laminating direction to form a molten metal region at the interface between the ceramic substrate and the metal plate;
A solidification step of joining the ceramic substrate and the metal plate by solidifying the molten metal region;
In the fixing step, Cu and the additive element are interposed in the interface between the ceramic substrate and the metal plate within a range of 0.1 mg / cm ^{2 to} 10 mg / cm ² ,
In the heating step, the molten metal region is formed at the interface between the ceramic substrate and the metal plate by diffusing elements of the fixed layer toward the metal plate side. Production method.   The method for manufacturing a power module substrate according to claim 6, wherein in the fixing step, Al is fixed together with Cu and the additive element.   The fixing step may be performed on at least one of the bonding surface of the ceramic substrate and the bonding surface of the metal plate by plating, vapor deposition, CVD, sputtering, cold spray, or application of a paste and ink in which powder is dispersed. Cu, and one or two or more additive elements selected from Zn, Ge, Ag, Mg, Ca, Ga and Li are fixed together. A method for manufacturing a power module substrate.

Images