JP5957848B2 - Power module substrate, power module substrate with heat sink, and method for manufacturing power module substrate - Google Patents

Description

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

Among semiconductor elements, a power element for supplying electric power has a relatively high calorific value, and for example, AlN (aluminum nitride), Al ₂ O ₃ (alumina), Si ₃ N ₄ ( A power module substrate in which a circuit layer is formed on one surface side of a ceramic substrate made of silicon nitride and the like and a metal layer is formed on the other surface side of the ceramic substrate is used. In this power module substrate, a heat sink is connected via a metal layer to form a power module substrate with a heat sink. Moreover, a semiconductor element as a power element is mounted on the circuit layer via a solder layer to form a power module.

As the above-described power module substrate, for example, in Patent Document 1, an aluminum plate is brazed to one surface of a ceramic substrate to form a circuit layer, and an aluminum plate is brazed to the other surface of the ceramic substrate to form a metal layer. What has been proposed.
In Patent Document 2, a metal plate is joined to one surface of a ceramic substrate to form a circuit layer, and an aluminum layer is formed by casting on the other surface side of the ceramic substrate to form a metal layer. A substrate is disclosed.

  In the power module described above, a heat cycle is loaded during use. Then, thermal stress acts on the bonding interface between the ceramic substrate and the circuit layer and the metal layer due to the difference in thermal expansion coefficient between the ceramic substrate and aluminum, and the bonding reliability between the ceramic substrate and the circuit layer and metal layer decreases. There was a risk. Here, the circuit layer and the metal layer are made of a metal having a relatively small deformation resistance such as aluminum having a purity of 99.99% by mass or more (so-called 4N aluminum), and the thermal stress is absorbed by the deformation of the circuit layer and the metal layer. As a result, it is possible to improve the bonding reliability.

By the way, when the circuit layer is made of a metal having a relatively small deformation resistance such as 4N aluminum, there is a problem that undulations and wrinkles are generated on the surface of the circuit layer when a thermal cycle is applied. When waviness or wrinkles occur on the surface of the circuit layer, cracks occur in the solder layer, and the reliability of the power module is reduced.
In particular, recently, Sn-Ag-based and Sn-Cu-based lead-free solder materials are often used as solder layers from the viewpoint of environmental load. These lead-free solder materials are less likely to be deformed than conventional Sn-Pb solder materials, and cracks tend to occur in the solder layer due to waviness and wrinkles of the circuit layer.
Recently, power modules have become smaller and thinner, and the usage environment has become harsh, and the amount of heat generated from electronic components such as semiconductor elements has increased. Therefore, undulations and wrinkles tend to occur on the surface of the circuit layer.

  Here, for example, Patent Documents 1 and 2 disclose one using a copper plate as a circuit layer. When the circuit layer is made of a copper plate, the deformation resistance of the copper plate is larger than that of aluminum, so that it is possible to suppress the occurrence of waviness and wrinkles in the circuit layer.

Japanese Patent No. 3171234 Japanese Patent Laid-Open No. 2002-075651

  By the way, as in Patent Documents 1 and 2, when the circuit layer is formed of a copper plate, the copper plate is hardened and hard to be deformed by a thermal cycle. Then, there is a possibility that the thermal stress acts on the ceramic substrate without being absorbed by the circuit layer, and the ceramic substrate is broken. When the ceramic substrate is cracked, the semiconductor element and circuit layer located on one side of the ceramic substrate are electrically connected to the metal layer and heat sink located on the other side of the ceramic substrate, and used as a power module substrate. You will not be able to. For this reason, when a copper plate is used as the circuit layer, it is necessary to increase the thickness of the ceramic substrate or improve the strength of the ceramic substrate.

  The present invention has been made in view of the above-described circumstances, and ensures insulation between one side and the other side of the ceramic substrate even if the circuit layer is made of copper or copper alloy having a large deformation resistance. An object of the present invention is to provide a power module substrate that can be used, a power module substrate with a heat sink using the power module substrate, and a method for manufacturing the power module substrate.

In order to solve such problems and achieve the above-mentioned object, the power module substrate of the present invention has a circuit layer formed on one surface side of the ceramic substrate, and an electron is formed on one surface of the circuit layer. A power module substrate on which a component is mounted, wherein the circuit layer is made of copper or a copper alloy, and a metal layer made of aluminum or an aluminum alloy is formed on the other surface of the ceramic substrate, Between the ceramic substrate and the circuit layer, a buffer aluminum layer made of aluminum or an aluminum alloy bonded to one surface of the ceramic substrate, an auxiliary ceramic plate bonded to the other surface of the circuit layer, There is interposed, said the ceramic substrate and the auxiliary ceramic plate are made of the same material, the auxiliary ceramic plate, A plurality of slits are characterized by being provided penetrating in the direction.

In the power module substrate having this configuration, since the circuit layer is made of copper or a copper alloy, deformation resistance is large, and even when a thermal cycle is applied, undulations and wrinkles are hardly generated on the surface of the circuit layer. Therefore, it is possible to suppress the occurrence of cracks in the solder layer.
Between the ceramic substrate and the circuit layer, a buffer aluminum layer made of aluminum or an aluminum alloy bonded to one surface of the ceramic substrate and an auxiliary ceramic bonded to the other surface of the circuit layer Since the board is interposed, the thermal stress caused by the difference in thermal expansion coefficient between the circuit layer and the ceramic substrate can be absorbed by the buffer aluminum layer, and the ceramic substrate can be prevented from cracking. Therefore, insulation can be ensured on one side and the other side of the ceramic substrate. In the auxiliary ceramic plate, cracks may occur due to thermal stress caused by the difference in thermal expansion coefficient from the circuit layer, but even if the buffer aluminum layer and the circuit layer are electrically connected, the ceramic substrate Can be used as a power module substrate.
In addition, since a metal layer made of aluminum or an aluminum alloy is formed on the other surface of the ceramic substrate, when a metal member such as a heat sink is joined to the other side of the ceramic substrate, the metal member and the ceramic substrate Thermal stress resulting from the difference in thermal expansion coefficient can be absorbed by the metal layer.

Further, since the auxiliary ceramic plate is provided with a plurality of slits penetrating in the thickness direction , the auxiliary ceramic plate is easily deformed. Therefore, the circuit layer and the ceramic plate are deformed by the deformation of the buffer aluminum layer and the auxiliary ceramic plate. The thermal stress resulting from the difference in thermal expansion coefficient with the substrate can be absorbed efficiently, and cracking of the ceramic substrate can be reliably prevented.
Furthermore, by forming slits in the auxiliary ceramic plate in advance, it is possible to prevent the auxiliary ceramic plate from being irregularly cracked due to thermal stress.

It is preferable that the buffer aluminum layer is made of aluminum having a purity of 99.98% by mass or more.
In this case, the deformation resistance of the buffer aluminum layer is reduced, and thermal stress can be efficiently absorbed by the deformation of the buffer aluminum layer.

The thickness tc of the circuit layer is 0.1 mm ≦ tc ≦ 3 mm, the thickness ts of the auxiliary ceramic plate is 0.15 mm ≦ ts ≦ 1 mm, and the thickness ta of the buffer aluminum layer is 0 It is preferable that 4 mm ≦ ta ≦ 3 mm.
In this case, since the thickness tc of the circuit layer is tc ≧ 0.1 mm, the conductivity in the circuit layer can be ensured. Further, since the thickness tc of the circuit layer is set to tc ≦ 3 mm, the deformation resistance of the circuit layer does not increase more than necessary, and the generated thermal stress can be suppressed.
Moreover, since the thickness ts of the auxiliary ceramic plate is set to ts ≧ 0.15 mm, the auxiliary ceramic plate can be reliably bonded to the circuit layer. Further, since the thickness ts of the auxiliary ceramic plate is set to ts ≦ 1 mm, the thermal resistance can be suppressed and heat can be efficiently dissipated.
Furthermore, since the thickness ta of the buffer aluminum layer is ta ≧ 0.4 mm, thermal stress can be reliably absorbed in the buffer aluminum layer. Further, since the thickness ta of the buffer aluminum layer is set to ta ≦ 3 mm, the thermal resistance can be suppressed and the heat can be efficiently dissipated.

A power module substrate with a heat sink according to the present invention includes the above-described power module substrate and a heat sink disposed on the other surface side of the power module substrate.
According to the power module substrate with a heat sink having this configuration, the ceramic substrate is prevented from being cracked, so that an electronic component such as a semiconductor element disposed on one side of the ceramic substrate and the other side of the ceramic substrate are disposed. Insulation can be ensured with the heat sink.

  The method for manufacturing a power module substrate according to the present invention is a method for manufacturing a power module substrate for producing the power module substrate described above, wherein the copper plate joining the circuit board and the auxiliary ceramic plate is joined. And an aluminum plate joining step for joining the auxiliary ceramic plate and the aluminum plate to be the buffer aluminum layer. In the copper plate joining step, the copper plate and the auxiliary ceramic plate are mixed at a solid phase temperature. It is set as the structure joined using the joining material made into less than melting | fusing point of the said aluminum plate, The said copper plate joining process and the said aluminum plate joining process are performed simultaneously, It is characterized by the above-mentioned.

  According to the method for manufacturing a power module substrate having this configuration, the copper plate joining step for joining the copper plate serving as the circuit layer and the auxiliary ceramic plate, and the aluminum plate serving as the buffer aluminum layer are joined to the auxiliary ceramic plate. Since it is set as the structure which performs the aluminum plate joining process to perform simultaneously, it can suppress that a curvature arises in an auxiliary ceramic board. Further, since the copper plate and the auxiliary ceramic plate are bonded using a bonding material whose solid-phase temperature is lower than the melting point of the aluminum plate, even if the temperature condition is lower than the melting point of the aluminum plate, the auxiliary ceramic plate A board and a copper board can be joined reliably.

The aluminum plate joining step is a kind selected from Si, Cu, Zn, Ge, Ag, Mg, Ca, Ga and Li on at least one of the joining surface of the auxiliary ceramic plate and the joining surface of the aluminum plate. Or a fixing step of fixing two or more kinds of additional elements and forming a fixing layer containing the additional element; a stacking step of stacking the auxiliary ceramic plate and the aluminum plate via the fixing layer; By pressing and heating the auxiliary ceramic plate and the aluminum plate in the stacking direction to form a molten metal region at the interface between the auxiliary ceramic plate and the aluminum plate, and solidifying the molten metal region A solidification step of joining the auxiliary ceramic plate and the aluminum plate, and in the heating step, The elements of the pinned layer be diffused in the aluminum plate side, the interface between the auxiliary ceramic plate and the aluminum plate may be configured to form the molten metal area.
In this case, since the aluminum plate serving as the buffer aluminum layer and the auxiliary ceramic plate are bonded by a so-called liquid phase diffusion bonding method, the buffer aluminum layer and the auxiliary ceramic plate are firmly bonded. be able to.

A ceramic substrate bonding step for bonding the buffer aluminum layer and the ceramic substrate may be included, and the copper plate bonding step, the aluminum plate bonding step, and the ceramic substrate bonding step may be performed simultaneously.
In this case, by simultaneously performing the ceramic substrate bonding step for bonding the buffer aluminum layer and the ceramic substrate, the copper plate bonding step, and the aluminum plate bonding step, the manufacturing process can be omitted and the manufacturing cost can be reduced. Can do.

  According to the present invention, even if the circuit layer is made of copper or a copper alloy having a large deformation resistance, the power module substrate that can ensure insulation on one side and the other side of the ceramic substrate, and this power module It is possible to provide a power module substrate with a heat sink using the working substrate and a method for manufacturing the power module substrate.

It is a schematic explanatory drawing of the power module using the board | substrate for power modules which is the 1st Embodiment of this invention. It is a flowchart of the manufacturing method of the power module shown in FIG. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules which is the 1st Embodiment of this invention. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules which is the 1st Embodiment of this invention. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules with a heat sink which is the 1st Embodiment of this invention. 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 explanatory drawing which shows the density | concentration distribution of the addition element in the interface with the auxiliary ceramic board of the buffer aluminum layer of the board | substrate for power modules which is the 2nd Embodiment of this invention. It is explanatory drawing which shows the density | concentration distribution of the additive element in the buffer aluminum layer and ceramics board | substrate of the power module board | substrate which is the 2nd Embodiment of this invention, and the interface of a ceramics board | substrate and a metal layer. It is explanatory drawing which shows the density | concentration distribution of the addition element in the metal layer and heat sink (heat sink) of the board | substrate for power modules (power module board | substrate with a heat sink) which is the 2nd Embodiment of this invention. It is a flowchart of the manufacturing method of the power module which is the 2nd Embodiment of this invention. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules (power module board | substrate with a heat sink) which is the 2nd Embodiment of this invention. It is explanatory drawing which shows the joining interface vicinity of the buffer aluminum layer in FIG. 11, and an auxiliary | assistant ceramic board. It is explanatory drawing which shows the joining interface vicinity of the buffer aluminum layer and ceramic substrate in FIG. 11, and a ceramic substrate and a metal layer. It is explanatory drawing which shows the joining interface vicinity of the metal layer and heat sink in FIG. In an Example, it is upper surface explanatory drawing which shows the measuring method of the electrical resistance value of the thickness direction of the board | substrate for power modules. In an Example, it is side explanatory drawing which shows the measuring method of the electrical resistance value of the thickness direction of the board | substrate for power modules.

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 the 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 element 3 bonded to the surface of the circuit layer 12 via a solder layer 2, and the other side of the power module substrate 10 ( And a heat sink 40 disposed on the lower side in FIG. 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 includes a ceramic substrate 11, a circuit layer 12 disposed on one surface side (upper side in FIG. 1) of the ceramic substrate 11, and the other surface (lower surface in FIG. 1). And a metal layer 13 bonded to each other.
Between the ceramic substrate 11 and the circuit layer 12, the buffer aluminum layer 16 made of aluminum or aluminum alloy bonded to one surface of the ceramic substrate 11 and the one surface of the buffer aluminum layer 16 are bonded. In addition, an auxiliary ceramic plate 17 bonded to the other surface of the circuit layer 12 is disposed.

The ceramic substrate 11 prevents electrical connection between the circuit layer 12 disposed on one surface side and the metal layer 13 disposed on the other surface side, and is a highly insulating AlN. (Aluminum nitride). Further, the thickness t ₀ of the ceramic substrate 11 is set in a range of 0.2 mm ≦ t ₀ ≦ 1.5 mm, and in this embodiment, t ₀ = 0.635 mm.

  As shown in FIG. 4, the metal layer 13 is formed by joining an aluminum plate 23 made of aluminum or an aluminum alloy to the other surface of the ceramic substrate 11. In the present embodiment, the metal layer 13 is formed by bonding a metal plate 23 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99 mass% or more to the ceramic substrate 11.

As shown in FIG. 3, the circuit layer 12 is formed by bonding a copper plate 22 made of copper or a copper alloy to one surface of the auxiliary ceramic plate 17. In the present embodiment, the circuit layer 12 is formed of oxygen-free copper.
The thickness tc of the circuit layer 12 is 0.1 mm ≦ tc ≦ 3 mm, and in this embodiment, tc = 1.0 mm.

As shown in FIG. 3, the buffer aluminum layer 16 is formed by joining an aluminum plate 26 made of aluminum or an aluminum alloy to the other surface of the auxiliary ceramic plate 17. The buffer aluminum layer 16 can be made of aluminum or an aluminum alloy. In the present embodiment, the buffer aluminum layer 16 is formed by joining an aluminum plate 26 having a purity of 99.99% by mass or more to the auxiliary ceramic plate 17.
Further, the thickness ta of the buffer aluminum layer 16 is 0.4 mm ≦ ta ≦ 3 mm, and in this embodiment, ta = 2.0 mm.

The auxiliary ceramic plate 17 is made of a ceramic material such as AlN, Al ₂ O ₃ , or Si ₃ N ₄ , and is made of AlN (aluminum nitride) in the present embodiment. The thickness ts of the auxiliary ceramic plate 17 is set in a range of 0.15 mm ≦ ts ≦ 1 mm, and in the present embodiment, ts = 0.635 mm.
In the present embodiment, as shown in FIG. 1 or FIG. 3, the auxiliary ceramic plate 17 is provided with a plurality of slits 18 extending in the thickness direction. Are divided in advance.

  The heat sink 40 is for cooling the power module substrate 10 described above, and a top plate portion 41 joined to the power module substrate 10 and a flow path 42 for circulating a cooling medium (for example, cooling water). And. The heat sink 40 (top plate portion 41) is preferably made of a material having good thermal conductivity, and is made of A6063 (aluminum alloy) in the present embodiment.

Below, the manufacturing method of the board | substrate 10 for power modules which is this embodiment, the board | substrate for power modules with a heat sink, and the power module 1 is demonstrated with reference to FIGS.
As shown in FIG. 2, the manufacturing method of the power module 1 includes a copper plate joining step S01 for joining the copper plate 22 and the auxiliary ceramic plate 17, and an aluminum plate joining step S02 for joining the auxiliary ceramic plate 17 and the aluminum plate 26. A ceramic substrate bonding step S03 for bonding the buffer aluminum layer 16 and the ceramic substrate 11 and the aluminum plate 23 to be the ceramic substrate 11 and the metal layer 13, and a heat sink bonding step S04 for bonding the power module substrate 10 and the heat sink 40. And a semiconductor element bonding step S05 for bonding the semiconductor element 3 to one surface of the circuit layer 12.

(Copper plate joining step S01 / aluminum plate joining step S02)
First, as shown in FIG. 3, the copper plate 22 is laminated on one surface side (the upper side in FIG. 3) of the auxiliary ceramic plate 17 via the brazing material 50. Further, the aluminum plate 26 is laminated on the other surface side (lower side in FIG. 3) of the auxiliary ceramic plate 17 via the first brazing material 51.
Here, the first brazing material 51 interposed between the aluminum plate 26 and the auxiliary ceramic plate 17 is made of an Al—Si alloy, and in the present embodiment, is made of Al—7.5 mass% Si. A brazing material foil having a thickness of 5 to 30 μm is used.

  The brazing material 50 interposed between the copper plate 22 and the auxiliary ceramic plate 17 has a solid phase temperature lower than the melting point of the aluminum plate 26. Specifically, the brazing material 50 is configured such that one or more low melting point elements selected from In, Bi, Li, and Sn are added to an Ag—Cu—Ti alloy. In the present embodiment, an Ag-24 mass% Cu-2 mass% Ti-14 mass% In alloy is used. The brazing material 50 has a thickness of 10 to 100 μm.

Next, the laminated copper plate 22, the auxiliary ceramic plate 17, and the aluminum plate 26 are charged and heated in a vacuum heating furnace in a state of being pressurized (pressure 1.5 to 35 kgf / cm ² ) in the lamination direction, A molten metal region 60 is formed at the interface between the copper plate 22 and the auxiliary ceramic plate 17, and a first molten metal region 61 is formed at the interface between the auxiliary ceramic plate 17 and the aluminum plate 26.
Here, in this embodiment, the pressure in the vacuum heating furnace is set in the range of 10 ⁻⁶ Pa to 10 ⁻³ Pa, and the heating temperature is set in the range of 630 ° C. to 655 ° C.

  Next, the copper plate 22 and the auxiliary ceramic plate 17 and the auxiliary ceramic plate 17 and the aluminum plate 26 are joined by solidifying the molten metal region 60 and the first molten metal region 61 described above. That is, in this embodiment, the copper plate joining step S01 and the aluminum plate joining step S02 are performed simultaneously.

(Ceramic substrate bonding step S03)
Next, as shown in FIG. 4, the ceramic substrate 11 is laminated on the other surface side of the buffer aluminum layer 16 via the second brazing material 52, and the third brazing material 53 is disposed on the other surface side of the ceramic substrate 11. Then, an aluminum plate 23 to be the metal layer 13 is laminated.
Here, the second brazing material 52 and the third brazing material 53 are made of an Al-7.5 mass% Si alloy in this embodiment. Moreover, the thickness of the 2nd brazing material 52 and the 3rd brazing material 53 shall be 5-30 micrometers.

The laminated circuit layer 12, auxiliary ceramic plate 17, buffer aluminum layer 16, ceramic substrate 11 and aluminum plate 23 are pressed in the stacking direction (pressure 1.5 to 35 kgf / cm ² ) in a vacuum heating furnace. The second molten metal region 62 is formed between the buffer aluminum layer 16 and the ceramic substrate 11, and the third molten metal region 63 is formed between the ceramic substrate 11 and the aluminum plate 23.
Here, in this embodiment, the pressure in the vacuum heating furnace is set in the range of 10 ⁻⁶ Pa to 10 ⁻³ Pa, and the heating temperature is set in the range of 630 ° C. to 655 ° C.

Next, the buffer aluminum layer 16 and the ceramic substrate 11, and the ceramic substrate 11 and the aluminum plate 23 are joined by solidifying the second molten metal region 62 and the third molten metal region 63 described above.
In this way, the power module substrate 10 according to the present embodiment is produced.

(Heat sink joining step S04)
Next, as shown in FIG. 5, the heat sink 40 is laminated on the other side (the lower side in FIG. 5) of the metal layer 13 of the power module substrate 10 via the fourth brazing material 54. The fourth brazing material 54 is made of an alloy having a lower solid phase temperature than the second brazing material 52 and the third brazing material 53, and is an Al-10 mass% Si alloy in this embodiment. The thickness of the fourth brazing material 54 is 50 to 100 μm.

The laminated power module substrate 10 and the heat sink 40 are charged in a stacking direction (pressure 1.5 to 20 kgf / cm ² ) and charged in a vacuum heating furnace to be heated, and the metal layer 13 and the heat sink 40 are heated. The 4th molten metal area | region 64 is formed between these.
Then, the heat sink 40 and the power module substrate 10 are joined by solidifying the fourth molten metal region 64. In this way, the power module substrate with a heat sink according to the present embodiment is produced.

(Semiconductor element bonding step S05)
Next, the semiconductor element 3 is placed on a Ni plating layer (not shown) formed on the surface of the circuit layer 12 via a solder material, and soldered in a reduction furnace. Thereby, the semiconductor element 3 is joined on the board | substrate 10 for power modules via the solder layer 2, and the power module 1 which is this embodiment is produced.

  According to the present embodiment configured as described above, since the circuit layer 12 is configured by the copper plate 22 having a relatively large deformation resistance, the occurrence of waviness and wrinkles on the surface of the circuit layer 12 can be suppressed. it can. Therefore, even when a lead-free solder material is used, the occurrence of cracks in the solder layer 2 can be suppressed.

  Since the buffer aluminum layer 16 and the auxiliary ceramic plate 17 are interposed between the ceramic substrate 11 and the circuit layer 12, heat caused by the difference in thermal expansion coefficient between the circuit layer 12 and the ceramic substrate 11. The stress can be absorbed by the buffer aluminum layer 16, and the ceramic substrate 11 can be prevented from cracking. Therefore, insulation can be ensured on one side and the other side of the ceramic substrate 11.

Further, in the present embodiment, since the auxiliary ceramic plate 17 is provided with a plurality of slits 18 extending in the thickness direction, the auxiliary ceramic plate 17 is easily deformed, and the buffer aluminum layer 16 and the auxiliary aluminum plate 16 are supported. The deformation of the ceramic plate 17 can efficiently absorb the thermal stress caused by the difference in thermal expansion coefficient between the circuit layer 12 and the ceramic substrate 11. Furthermore, by forming slits in the auxiliary ceramic plate 17 in advance, it is possible to prevent the auxiliary ceramic plate 17 from being irregularly cracked due to thermal stress.
Furthermore, in this embodiment, since the buffer aluminum layer 16 is made of 4N aluminum, the deformation resistance of the buffer aluminum layer 16 is reduced, and the deformation of the buffer aluminum layer 16 efficiently absorbs thermal stress. be able to.

In addition, since the thickness tc of the circuit layer 12 is 0.1 mm ≦ tc ≦ 3 mm and tc = 1.0 mm in this embodiment, the conductivity in the circuit layer 12 can be ensured. The deformation resistance of the circuit layer 12 does not increase more than necessary, and the occurrence of cracks in the ceramic substrate 11 can be suppressed.
Furthermore, since the thickness ts of the auxiliary ceramic plate 17 is 0.15 mm ≦ ts ≦ 1 mm, and in this embodiment, ts = 0.635 mm, it is possible to reliably bond to the circuit layer 12. The thermal resistance in the stacking direction can be suppressed, and heat can be efficiently dissipated toward the heat sink 40 side.
Further, the thickness ta of the buffer aluminum layer 16 is set to 0.4 mm ≦ ta ≦ 3 mm, and in this embodiment, ta = 2.0 mm. Therefore, the buffer aluminum layer 16 reliably absorbs thermal stress. In addition, thermal resistance in the stacking direction can be suppressed, and heat can be efficiently dissipated toward the heat sink 40 side.

  In the present embodiment, the metal layer 13 made of aluminum or aluminum alloy is formed on the other surface of the ceramic substrate 11, and the heat sink 40 is joined via the metal layer 13. The thermal stress resulting from the difference in thermal expansion coefficient with the ceramic substrate 11 can be absorbed by the metal layer 13, thereby preventing the ceramic substrate 11 from cracking and improving the bonding reliability between the heat sink 40 and the ceramic substrate 11. be able to.

In the present embodiment, the copper plate bonding step S01 for forming the circuit layer 12 and the aluminum plate bonding step S02 for forming the buffer aluminum layer 16 are performed at the same time. Can be suppressed.
In the copper plate joining step S01, since the brazing material 50 having a solid phase temperature lower than the melting point of the aluminum plate 26 is used, the copper plate 22 and the auxiliary ceramic plate 17 are bonded even under temperature conditions lower than the melting point of the aluminum plate 26. It can be reliably joined.
In the present embodiment, as the brazing material 50, an alloy in which one or more low melting point elements selected from In, Bi, Li, and Sn are added to an Ag—Cu—Ti alloy, specifically, Since an Ag-24 mass% Cu-2 mass% Ti-14 mass% In alloy is used, the solid phase temperature is 620 ° C., and the copper plate 22 and the auxiliary ceramic plate 17 are bonded under temperature conditions below the melting point of the aluminum plate 26. It can be firmly joined.

Next, a second embodiment of the present invention will be described with reference to FIGS.
The power module 101 according to this embodiment includes a power module substrate 110 on which a circuit layer 112 is disposed, a semiconductor element 103 bonded to the surface of the circuit layer 112 via a solder layer 102, and a power module substrate 110. And a heat sink 140 disposed on the other side (lower side in FIG. 6). Here, the solder layer 102 is made of, for example, Sn—Ag, Sn—In, or Sn—Ag—Cu solder. In the present embodiment, a Ni plating layer (not shown) is provided between the circuit layer 112 and the solder layer 102.

The power module substrate 110 includes a ceramic substrate 111, a circuit layer 112 disposed on one surface side (upper side in FIG. 6) of the ceramic substrate 111, and the other surface (lower surface in FIG. 6). And a metal layer 113 bonded to each other.
Between the ceramic substrate 111 and the circuit layer 112, the buffer aluminum layer 116 bonded to one surface of the ceramic substrate 111, and the other of the circuit layer 112 bonded to one surface of the buffer aluminum layer 116 Auxiliary ceramic plate 117 joined to the surface is disposed.

The ceramic substrate 111 prevents electrical connection between the circuit layer 112 disposed on one surface side and the metal layer 113 on the other surface side, and is a highly insulating Al ₂ O ₃ ( (Alumina). In addition, the thickness t ₀ of the ceramic substrate 111 is set in a range of 0.2 mm ≦ t ₀ 1 ≦ 1.5 mm, and in this embodiment, t ₀ = 0.635 mm.

  As shown in FIG. 11, the metal layer 113 is formed by joining an aluminum plate 123 made of aluminum or an aluminum alloy to the other surface of the ceramic substrate 111. In the present embodiment, the metal layer 113 is formed by bonding an aluminum plate 123 having a purity of 99.99% by mass or more to the ceramic substrate 111.

As shown in FIG. 11, the circuit layer 112 is formed by bonding a copper plate 122 made of copper or a copper alloy to one surface of the auxiliary ceramic substrate 117. In the present embodiment, the circuit layer 112 is made of oxygen-free copper.
In addition, the thickness tc of the circuit layer 112 is 0.1 mm ≦ tc ≦ 0.6 mm, and in this embodiment, tc = 1.0 mm.

As shown in FIG. 11, the buffer aluminum layer 116 is formed by joining an aluminum plate 126 made of aluminum or an aluminum alloy to the other surface of the auxiliary ceramic plate 117. The buffer aluminum layer 116 can be made of aluminum or an aluminum alloy. In this embodiment, the buffer aluminum layer 116 is formed by joining an aluminum plate 126 having a purity of 99.99% by mass or more to the auxiliary ceramic plate 117.
In addition, the thickness ta of the buffer aluminum layer 116 is set to 0.4 mm ≦ ta ≦ 3.0 mm, and in this embodiment, ta = 1.5 mm.

The auxiliary ceramic plate 117 is made of a ceramic material such as AlN, Al ₂ O ₃ , or Si ₃ N ₄ , and is made of Al ₂ O ₃ (alumina) in the present embodiment. The thickness ts of the auxiliary ceramic plate 117 is set within a range of 0.15 mm ≦ ts ≦ 1 mm, and in the present embodiment, ts = 0.3 mm.

  The heat sink 140 is for cooling the power module substrate 110 described above. In the present embodiment, the heat sink 140 is a heat radiating plate made of aluminum or an aluminum alloy.

As shown in FIG. 7, at the bonding interface between the auxiliary ceramic plate 117 and the buffer aluminum layer 116, one or two selected from Si, Cu, Zn, Ge, Ag, Mg, Ca, Ga and Li are used. Additive elements of seeds or more are in solid solution, and in this embodiment, Cu is dissolved as an additive element.
Here, in the vicinity of the bonding interface between the buffer aluminum layer 116 and the auxiliary ceramic plate 117, the concentration gradient layer 171 in which the concentration of the additive element (Cu concentration in this embodiment) gradually decreases as the distance from the bonding interface in the stacking direction increases. Is formed. Further, the concentration of the additive element (Cu concentration in the present embodiment) on the bonding interface side of the concentration gradient layer 171 (near the bonding interface of the buffer aluminum layer 116 with the auxiliary ceramic plate 117) is 0.01 mass% or more and 5 mass. % Is set within the range.
The concentration of the additive element in the vicinity of the bonding interface between the buffer aluminum layer 116 and the auxiliary ceramic plate 117 is an average value measured at 50 points from the bonding interface by EPMA analysis (spot diameter 30 μm). In the graph of FIG. 7, line analysis is performed in the stacking direction in the central portion of the buffer aluminum layer 116, and the Cu concentration on the vertical axis is obtained on the basis of the Cu concentration at the 50 μm position.

Further, as shown in FIG. 8, at the bonding interface between the buffer aluminum layer 116 and the ceramic substrate 111 and between the ceramic substrate 111 and the metal layer 113, Si, Cu, Zn, Ge, Ag, Mg, Ca, Ga, and Li are used. One or more selected additive elements are in solid solution, and in the present embodiment, Cu is dissolved as the additive element.
Here, in the vicinity of the bonding interface between the buffer aluminum layer 116 and the metal layer 113 and the ceramic substrate 111, the concentration of the additive element (Cu concentration in the present embodiment) gradually decreases as the distance from the bonding interface in the stacking direction increases. Inclined layers 172 and 173 are formed. Further, the concentration (Cu concentration in this embodiment) of the additive element on the bonding interface side of the concentration gradient layers 172 and 173 (near the bonding interface between the buffer aluminum layer 116 and the metal layer 113 with the ceramic substrate 111) is 0.01. It is set within a range of mass% to 5 mass%.
In addition, the concentration of the additive element in the vicinity of the bonding interface between the buffer aluminum layer 116 and the metal layer 113 with the ceramic substrate 111 is an average value measured at 50 points from the bonding interface by EPMA analysis (spot diameter 30 μm). . In the graph of FIG. 8, line analysis is performed in the stacking direction in the central portion of the buffer aluminum layer 116 and the metal layer 113, and the Cu concentration on the vertical axis is obtained on the basis of the Cu concentration at the 50 μm position. .

Furthermore, as shown in FIG. 9, at the bonding interface between the metal layer 113 and the heat sink 140, the metal layer 113 and the heat sink 140 are selected from Si, Cu, Zn, Ge, Ag, Mg, Ca, Ga, and Li. One or more additional elements are in solid solution, and in this embodiment, Cu is dissolved as the additional element.
Here, in the vicinity of the bonding interface between the metal layer 113 and the heat sink 140, concentration gradient layers 174 and 175 in which the concentration of the additive element (Cu concentration in the present embodiment) gradually decreases as the distance from the bonding interface in the stacking direction is formed. Has been. Further, the concentration of the additive element (Cu concentration in this embodiment) on the bonding interface side (near the bonding interface between the metal layer 113 and the heat sink 140) of the concentration gradient layers 174 and 175 is 0.01 mass% or more and 5 mass% or less. It is set within the range.
The concentration of the additive element in the vicinity of the bonding interface between the metal layer 113 and the heat sink 140 is an average value measured at 5 points from the bonding interface by EPMA analysis (spot diameter of 30 μm). In the graph of FIG. 9, line analysis is performed in the stacking direction in the central portion of the metal layer 113 and the heat sink 140, and the Cu concentration on the vertical axis is obtained on the basis of the Cu concentration at the 50 μm position.

Below, the manufacturing method of the board | substrate for power modules with a heat sink which is this embodiment, and the power module 101 is demonstrated with reference to FIGS.
The manufacturing method of this power module 101 includes a copper plate joining step S101 for joining the copper plate 122 and the auxiliary ceramic plate 117, and an aluminum plate joining step S102 for joining the auxiliary ceramic plate 111 and the aluminum plate 126 serving as the buffer aluminum layer 116. A ceramic substrate bonding step S103 for bonding the buffer aluminum layer 116 and the ceramic substrate 111, an aluminum plate 123 to be the ceramic substrate 111 and the metal layer 113, and a heat sink bonding step S104 for bonding the power module substrate 110 and the heat sink 140. And a semiconductor element bonding step S105 for bonding the semiconductor element 103 to one surface of the circuit layer 112.

(Copper plate bonding step S101 / aluminum plate bonding step S102 / ceramic substrate bonding step S103 / heat sink bonding step S104)
First, as shown in FIG. 11, the additive element (Cu) is fixed to one surface of the aluminum plate 126 by sputtering to form the first fixed layer 151, and the additive element is added to the other surface of the aluminum plate 126 by sputtering. The second fixing layer 152 is formed by fixing (Cu). Further, the additive element (Cu) is fixed to one surface of the aluminum plate 123 by sputtering to form the third fixed layer 153, and the additive element (Cu) is fixed to the other surface of the aluminum plate 123 by sputtering. A fourth fixing layer 154 is formed. Here, the amount of added elements in the first fixed layer 151, the second fixed layer 152, the third fixed layer 153, and the fourth fixed layer 154 is in the range of 0.01 mg / cm ^{2 to} 10 mg / cm ^2. In this embodiment, Cu is used as the additive element, and the amount of Cu in the first fixed layer 151, the second fixed layer 152, the third fixed layer 153, and the fourth fixed layer 154 is 0.08 mg / cm ² or more 2. 0.7 mg / cm ² or less.

Then, as shown in FIG. 11, the aluminum plate 126 is laminated on the other surface side (lower side in FIG. 11) of the auxiliary ceramic plate 117, and the ceramic substrate 111 is laminated on the other surface side of the aluminum plate 126, An aluminum plate 123 is laminated on the other surface side of the ceramic substrate 111, and a heat sink 140 is laminated on the other surface side of the aluminum plate 123.
Further, a copper plate 122 is laminated on one surface side (the upper side in FIG. 11) of the auxiliary ceramic plate 117 with a brazing material 150 interposed therebetween.

  Here, the brazing material 150 interposed between the copper plate 122 and the auxiliary ceramic plate 117 has a solid phase temperature below the melting point of the aluminum plates 123 and 126 and the heat sink 140. Specifically, the brazing material 150 is an alloy in which one or more low melting point elements selected from In, Bi, Li, and Sn are added to an Ag—Cu—Ti alloy. In the present embodiment, an Ag-24 mass% Cu-2 mass% Ti-14 mass% In alloy is used. The brazing material 150 has a thickness of 10 to 100 μm.

Next, the copper plate 122, the auxiliary ceramic plate 117, the aluminum plate 126, the ceramic substrate 111, the aluminum plate 123, and the heat sink 140 are pressed in the stacking direction (pressure 1 to 35 kgf / cm ² ) in the vacuum heating furnace. Charge and heat. Here, in this embodiment, the pressure in a vacuum heating furnace is set in the range of 10 < ^-3 > -10 < ^-6 > Pa, and the heating temperature is set in the range of 630 degreeC or more and 655 degrees C or less.

Then, the molten metal region 160 is formed at the interface between the copper plate 122 and the auxiliary ceramic plate 117 by melting the brazing material 150.
Further, a first molten metal region 161 is formed at the interface between the auxiliary ceramic plate 117 and the aluminum plate 126.
Further, a second molten metal region 162 is formed at the interface between the aluminum plate 126 and the ceramic substrate 111, and a third molten metal region 163 is formed at the interface between the ceramic substrate 111 and the aluminum plate 123.
Further, a fourth molten metal region 164 is formed at the interface between the aluminum plate 123 and the heat sink 140.

  Here, in the first molten metal region 161 formed at the interface between the auxiliary ceramic plate 117 and the aluminum plate 126, as shown in FIG. 12, the additive element (Cu) of the first fixing layer 151 is on the aluminum plate 126 side. By diffusion, the concentration (Cu concentration) of the additive element in the vicinity of the first fixed layer 151 of the aluminum plate 126 is increased, and the melting point is lowered.

  Further, the second molten metal region 162 formed at the interface between the aluminum plate 126 and the ceramic substrate 111 and the third molten metal region 163 formed at the interface between the ceramic substrate 111 and the aluminum plate 123 are as shown in FIG. Further, the additive element (Cu) of the second fixing layer 152 diffuses to the aluminum plate 126 side, and the additive element (Cu) of the third fixing layer 153 diffuses to the aluminum plate 123 side, whereby the second fixing layer of the aluminum plate 126 is obtained. It is formed by increasing the concentration of the additive element in the vicinity of 152 (Cu concentration) and the concentration of the additive element in the vicinity of the third fixed layer 153 of the aluminum plate 123 (Cu concentration) to lower the melting point.

  Further, as shown in FIG. 14, the fourth molten metal region 164 formed at the interface between the aluminum plate 123 and the heat sink 140 has an additive element (Cu) of the fourth fixing layer 154 on the aluminum plate 123 side and the heat sink 140 side. As a result, the concentration (Cu concentration) of the additive element in the vicinity of the fourth fixing layer 154 of the aluminum plate 123 and the heat sink 140 is increased, and the melting point is lowered.

Next, the temperature is kept constant in a state where the first molten metal region 161, the second molten metal region 162, the third molten metal region 163, and the fourth molten metal region 164 are formed.
Then, Cu in the 1st molten metal area | region 161, the 2nd molten metal area | region 162, the 3rd molten metal area | region 163, and the 4th molten metal area | region 164 further spread | diffused, and the 1st molten metal area | region 161 and the 2nd molten metal area | region 162, the third molten metal region 163, the portion of the fourth molten metal region 164, the Cu concentration gradually decreases, the melting point increases, and solidification proceeds while the temperature is kept constant. Go. Thereby, the auxiliary ceramic plate 117 and the aluminum plate 126, the aluminum plate 126 and the ceramic substrate 111, the ceramic substrate 111 and the aluminum plate 123, and the aluminum plate 123 and the heat sink 140 are joined.

That is, the auxiliary ceramic plate 117 and the aluminum plate 126, the aluminum plate 126 and the ceramic substrate 111, the ceramic substrate 111 and the aluminum plate 123, and the aluminum plate 123 and the heat sink 140 are joined by so-called liquid phase diffusion bonding (Transient Liquid Phase Bonding). -ing After solidification progresses in this way, cooling is performed to room temperature.
In the cooling process, the molten metal region 160 formed at the interface between the copper plate 122 and the auxiliary ceramic plate 117 is solidified, and the copper plate 122 and the auxiliary ceramic plate 117 are joined.

  In this manner, the copper plate 122, the auxiliary ceramic plate 117, the aluminum plate 126, the ceramic substrate 111, the aluminum plate 123, and the heat sink 140 are joined, and the power module substrate with a heat sink according to this embodiment is manufactured. That is, in this embodiment, the copper plate bonding step S101, the aluminum plate bonding step S102, the ceramic substrate bonding step S103, and the heat sink bonding step S104 are performed simultaneously.

(Semiconductor element bonding step S105)
Next, the semiconductor element 103 is placed on a Ni plating layer (not shown) formed on the surface of the circuit layer 112 via a solder material, and soldered in a reduction furnace. As a result, the semiconductor element 103 is bonded onto the power module substrate 110 via the solder layer 102, and the power module 101 according to this embodiment is manufactured.

According to the present embodiment configured as described above, since the circuit layer 112 is configured by the copper plate 122 and the metal layer 113 is configured by the aluminum plate 123, the same effect as the first embodiment is obtained. It becomes possible to play.
In the present embodiment, since the copper plate 123 to be the circuit layer 112, the ceramic substrate 111, the aluminum plate 123 to be the metal layer 113, and the heat sink 140 are joined at the same time, the ceramic at the time of joining is used. Generation of warpage of the substrate 111 can be suppressed. Moreover, the manufacturing cost of the power module substrate with a heat sink can be reduced.

  In the present embodiment, the auxiliary ceramic plate 117 and the buffer aluminum layer 116, and the buffer aluminum layer 116 and the ceramic substrate 111 are bonded by a so-called liquid phase diffusion bonding method. The aluminum layer 116 and the ceramic substrate 111 can be firmly bonded.

Furthermore, in this embodiment, since the ceramic substrate 111 and the aluminum plate 123 to be the metal layer 113 are also bonded by the liquid phase diffusion bonding method, the ceramic substrate 111 and the metal layer 113 are firmly bonded, and the bonding reliability is increased. It is possible to manufacture the power module substrate 10 having excellent properties.
Furthermore, in this embodiment, since the aluminum plate 123 and the heat sink 140 are also joined by the liquid phase diffusion joining method, the aluminum plate 123 and the heat sink 140 can be firmly joined.

In the present embodiment, since Cu as an additive element is dissolved in the buffer aluminum layer 116 in the vicinity of the bonding interface with the auxiliary ceramic plate 117 and in the vicinity of the bonding interface with the ceramic substrate 111, the buffer aluminum layer 116. The strength in the vicinity of the bonding interface can be improved.
Specifically, since the Cu concentration in the vicinity of the bonding interface between the auxiliary ceramic plate 117 and the ceramic substrate 111 in the buffer aluminum layer 116 is 0.05 mass% or more, the bonding interface side portion of the buffer aluminum layer 116 is Reinforcement can be ensured, and the occurrence of cracks in the buffer aluminum layer 116 can be prevented. Further, since the Cu concentration in the vicinity of the bonding interface between the auxiliary ceramic plate 117 and the ceramic substrate 111 in the buffer aluminum layer 116 is 5 mass% or less, the strength of the bonding interface of the buffer aluminum layer 116 becomes higher than necessary. Can be prevented. Therefore, the thermal stress when the thermal cycle is loaded on the power module substrate 110 can be absorbed by the buffer aluminum layer 116, and the ceramic substrate 111 can be prevented from cracking.

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 auxiliary ceramic plate and the ceramic substrate have been described by exemplifying those made of AlN and Al ₂ O ₃ , but are not limited to this, and are made of other ceramic materials such as Si ₃ N _4. It may be what was done.

  In the present embodiment, the description has been made assuming that one buffer aluminum layer and one auxiliary ceramic plate are interposed between the circuit layer and the ceramic substrate. However, the present invention is not limited to this. The buffer aluminum layer and a plurality of auxiliary ceramic plates may be interposed.

  Furthermore, in 1st Embodiment, although demonstrated as what provided the slit penetrated in the thickness direction in the auxiliary ceramic board, it is not limited to this, The groove part which does not penetrate in the thickness direction is formed. Also good. In this case, when a thermal stress is applied by the cooling / heating cycle, the auxiliary ceramic plate is cracked starting from the groove, and irregular cracking can be suppressed.

Moreover, in 2nd Embodiment, although Cu was fixed as an additional element and it demonstrated as what joins, it is not limited to this, Si, Cu, Ag, Zn, Mg, Ge, Ca, Ga, Any one or two or more additive elements of Li may be fixed.
When an easily oxidizable element such as Mg or Ca is used, it is preferable to fix the additive element together with aluminum. Thereby, it is possible to suppress oxidation wear of easily oxidizable elements such as Mg and Ca.

Further, in the second embodiment, it has been described that Cu is fixed to the aluminum plate. However, the present invention is not limited to this, and an additive element may be fixed to the auxiliary ceramic plate, the ceramic substrate, or the heat sink.
Furthermore, although it demonstrated as what fixes Cu by sputter | spatter, it is not limited to this, Cu is applied by plating, vapor deposition, CVD, cold spray, or application of paste or ink in which powder is dispersed. It may be fixed.

Further, in the present embodiment, the heat sink is described as being composed of the A6063 alloy, but is not limited thereto, and is composed of other metal materials such as A1100 alloy, A3003 alloy, A5052 alloy, and A7N01 alloy. It may be a thing.
Furthermore, the structure of the heat sink is not limited to this embodiment, and a heat sink having another structure may be adopted.

  In the present embodiment, the power module substrate is described as being bonded to the heat sink. However, the present invention is not limited to this, and a plurality of power module substrates are bonded to the heat sink. May be.

Below, the result of the confirmation experiment implemented in order to confirm the effect of this invention is demonstrated.
A power module substrate with a heat sink including a copper plate, an auxiliary ceramic plate, a buffer aluminum layer, a ceramic substrate, a metal layer, and a heat sink shown in Table 1 was produced and evaluated.

(Invention Example 1-6)
For joining the copper plate and the auxiliary ceramic plate, a brazing material made of an Ag-24 mass% Cu-2 mass% Ti-14 mass% In alloy and having a thickness of 50 μm was used.
For joining the auxiliary ceramic plate and the aluminum plate serving as the buffer aluminum layer, a brazing material made of an Al-7.5 mass% Si alloy and having a thickness of 20 μm was used.
A copper plate, an auxiliary ceramic plate, and an aluminum plate serving as a buffer aluminum layer were charged in a vacuum furnace (pressure 10 ⁻⁴ Pa, temperature 650 ° C.) in a state where the pressure was 15 kgf / cm ² in the stacking direction. And the auxiliary ceramic plate, the auxiliary ceramic plate and the aluminum plate serving as the buffer aluminum layer were bonded simultaneously.

Next, the buffer aluminum layer and the ceramic substrate, the aluminum plate that becomes the ceramic substrate and the metal layer, and the aluminum plate that becomes the metal layer and the heat sink are made of an Al-10 mass% Si alloy and have a thickness of 50 μm. Was used.
In a state where a copper plate, an auxiliary ceramic plate and a buffer aluminum layer, a ceramic substrate, an aluminum plate serving as a metal layer, and a heat sink are pressurized at a pressure of 3.5 kgf / cm ² in the stacking direction, a vacuum furnace (pressure 10 ^{− 4} Pa, temperature 610 ° C.), the buffer aluminum layer and the ceramic substrate, the aluminum plate serving as the ceramic substrate and the metal layer, and the aluminum plate serving as the metal layer and the heat sink were bonded simultaneously.
In Inventive Example 4-6, an auxiliary ceramic plate having a plurality of slits formed at intervals of 7 mm was used.

(Invention Example 7-12)
For joining the copper plate and the auxiliary ceramic plate, a brazing material made of an Ag-24 mass% Cu-2 mass% Ti-14 mass% In alloy and having a thickness of 50 μm was used.
Further, Cu was fixed by sputtering on both surfaces of the aluminum plate serving as the buffer aluminum layer and both surfaces of the aluminum plate serving as the metal layer. The fixed amount of Cu was 0.15 mg / cm ² .

In a state where a copper plate, an auxiliary ceramic plate, an aluminum plate serving as a buffer aluminum layer, a ceramic substrate, an aluminum plate serving as a metal layer, and a heat sink are stacked and pressed in a stacking direction at a pressure of 20 kgf / cm ² , a vacuum furnace ( Pressure 10 ⁻⁴ Pa, temperature 650 ° C.), copper plate and auxiliary ceramic plate, aluminum plate serving as auxiliary ceramic plate and buffer aluminum layer, aluminum plate serving as buffer aluminum layer and ceramic substrate, ceramic substrate and metal layer An aluminum plate to be formed, and an aluminum plate to be a metal layer and a heat sink were bonded simultaneously.
In Inventive Example 10-12, an auxiliary ceramic plate having a plurality of slits formed at intervals of 7 mm was used.

(Comparative Examples 1 and 2)
As a comparative example, a copper plate is bonded to one surface of a ceramic substrate, an aluminum plate serving as a metal layer is bonded to the other surface of the ceramic substrate, and a metal layer and a heat sink are bonded to each other. Was produced.

In Comparative Example 1, a brazing material made of an Ag-24 mass% Cu-2 mass% Ti-14 mass% In alloy and having a thickness of 50 μm was used for joining the copper plate and the ceramic substrate. In addition, a brazing material made of an Al-7.5 mass% Si alloy and having a thickness of 20 μm was used for joining the ceramic substrate and the aluminum plate serving as the metal layer.
A copper plate, a ceramic substrate, and an aluminum plate serving as a metal layer were charged in a vacuum furnace (pressure 10 ⁻⁴ Pa, temperature 650 ° C.) in a state where the pressure was 15 kgf / cm ² in the stacking direction. The board | substrate for ceramics and the aluminum board used as a metal layer were joined simultaneously, and the board | substrate for power modules was produced.

For joining the power module substrate and the heat sink, a brazing material made of an Al-10 mass% Si alloy and having a thickness of 50 μm was used. In a state where the power module substrate and the heat sink are pressurized in the laminating direction at a pressure of 3.5 kgf / cm ² , the substrate is inserted into a vacuum furnace (pressure 10 ⁻⁴ Pa, temperature 610 ° C.). Were joined.

In Comparative Example 2, a brazing material made of an Ag-24 mass% Cu-2 mass% Ti-14 mass% In alloy and having a thickness of 50 μm was used for joining the copper plate and the ceramic substrate.
Further, Cu was fixed to both surfaces of the aluminum plate to be the metal layer by sputtering. The fixed amount of Cu was 0.15 mg / cm ² .
A copper plate, a ceramic substrate, an aluminum plate serving as a metal layer, and a heat sink are stacked, and this is loaded in a vacuum furnace (pressure 10 ⁻⁴ Pa, temperature 650 ° C.) in a state where the pressure is 20 kgf / cm ² in the stacking direction. Then, a copper plate and a ceramic substrate, an aluminum plate serving as a ceramic substrate and a metal layer, and an aluminum plate serving as a metal layer and a heat sink were bonded simultaneously.

(Evaluation of electrical resistance before and after cooling cycle)
About the obtained substrate for power modules with a heat sink, the thermal cycle test was implemented and the change of the electrical resistance value before and behind the thermal cycle load was evaluated.
As shown in FIG. 15 and FIG. 16, the electrical resistance value is obtained by laminating a power module substrate with a heat sink using a tester (manufactured by KEITHLEY: 2010 MULTITIMER) between the center point A on the circuit layer and the point B on the heat sink. The electric resistance value in the direction was measured. The point B on the heat sink is the shortest end of the circuit layer from the point A and is on a straight line passing through the end A and the point A, and the distance H is equal to the distance H between the point A and the end. It was set as the point which made the perpendicular line on the heat sink from the place away from the edge part. Here, when the electrical resistance value was 10 ¹⁰ Ω or more, it was evaluated as ◯, and when it was less than 10 ⁸ Ω, it was evaluated as x.

  The cooling / heating cycle was performed using TSB-51 manufactured by Espec Co., Ltd. and using Fluorinert (manufactured by Sumitomo 3M Co., Ltd.) as the liquid phase. 3000 cycles were performed with -40 ° C. × 5 minutes ← → 125 ° C. × 5 minutes as one cycle. And the electrical resistance value before and behind a thermal cycle load was measured. The evaluation results are shown in Table 2.

(Observation of cracks on the outer periphery of ceramic substrates)
About the power module substrate with a heat sink after the thermal cycle load, the presence or absence of cracks in the outer peripheral portion of the ceramic substrate that can be observed from the appearance was observed. A case where a crack was observed in any of the outer peripheral portions of the ceramic substrate was evaluated as x, and a case where no crack was observed was evaluated as ◯. The evaluation results are shown in Table 2.

In the example of the present invention, it is confirmed that the electrical resistance value does not change greatly before and after the cooling / heating cycle load, and the insulation is ensured.
On the other hand, in Comparative Examples 1 and 2, the electrical resistance value is greatly reduced after the thermal cycle load, and it is confirmed that the electrical insulation value is not sufficiently insulated. This is presumed to be because the ceramic substrate was cracked.
From the above, according to the present invention, even if the circuit layer is made of a copper plate, the ceramic substrate can be prevented from cracking and insulation can be ensured.

1, 101 Power module 2, 102 Solder layer 3, 103 Semiconductor element (electronic component)
10, 110 Power module substrate 11, 111 Ceramic substrate 12, 112 Circuit layer 13, 113 Metal layer 16, 116 Buffer aluminum layer 17, 117 Auxiliary ceramic plate 18 Slit 40, 140 Heat sink 50, 150 Brazing material (joining material)

Claims (7)

A power module substrate in which a circuit layer is formed on one surface side of a ceramic substrate, and an electronic component is mounted on one surface of the circuit layer,
The circuit layer is made of copper or a copper alloy, and a metal layer made of aluminum or an aluminum alloy is formed on the other surface of the ceramic substrate.
Between the ceramic substrate and the circuit layer, a buffer aluminum layer made of aluminum or an aluminum alloy bonded to one surface of the ceramic substrate, and an auxiliary ceramic plate bonded to the other surface of the circuit layer; , Is intervening,
The ceramic substrate and the auxiliary ceramic plate are made of the same material ,
A substrate for a power module, wherein the auxiliary ceramic plate is provided with a plurality of slits penetrating in the thickness direction . 2. The power module substrate according to claim 1, wherein the buffer aluminum layer is made of aluminum having a purity of 99.98% by mass or more. The thickness tc of the circuit layer is 0.1 mm ≦ tc ≦ 3 mm, the thickness ts of the auxiliary ceramic plate is 0.15 mm ≦ ts ≦ 1 mm, and the thickness ta of the buffer aluminum layer is 0. The power module substrate according to claim 1, wherein 4 mm ≦ ta ≦ 3 mm. A power module substrate according to any one of claims 1 to 3, and a heat sink disposed on the other surface side of the power module substrate. Power module substrate. A method for producing a power module substrate for producing the power module substrate according to any one of claims 1 to 3 ,
A copper plate joining step for joining the copper plate serving as the circuit layer and the auxiliary ceramic plate, and an aluminum plate joining step for joining the auxiliary ceramic plate and an aluminum plate serving as the buffer aluminum layer,
In the copper plate joining step, the copper plate and the auxiliary ceramic plate are joined using a joining material whose solid phase temperature is less than the melting point of the aluminum plate,
The method for manufacturing a power module substrate, wherein the copper plate joining step and the aluminum plate joining step are performed simultaneously. The aluminum plate joining step is a kind selected from Si, Cu, Zn, Ge, Ag, Mg, Ca, Ga and Li on at least one of the joining surface of the auxiliary ceramic plate and the joining surface of the aluminum plate. Or a fixing step of fixing two or more kinds of additional elements and forming a fixing layer containing the additional element; a stacking step of stacking the auxiliary ceramic plate and the aluminum plate via the fixing layer; By pressing and heating the auxiliary ceramic plate and the aluminum plate in the stacking direction to form a molten metal region at the interface between the auxiliary ceramic plate and the aluminum plate, and solidifying the molten metal region A solidification step of joining the auxiliary ceramic plate and the aluminum plate, and in the heating step, The elements of the pinned layer be diffused in the aluminum plate side, the interface between the auxiliary ceramic plate and the aluminum plate, a power module substrate according to claim 5, characterized in that forming the molten metal region Manufacturing method. The buffer aluminum layer and has a ceramic substrate bonding step of bonding the ceramic substrate, according to claim 5 or claims and performing said copper plate bonding step and the aluminum plate bonding step and the ceramic substrate bonding step simultaneously Item 7. A method for manufacturing a power module substrate according to Item 6 .

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