JP5699442B2 - Power module substrate and power module - Google Patents

Description

  The present invention relates to a power module substrate and a power module used in a semiconductor device that controls a large current and a high voltage.

As a power module substrate on which a power element for power supply among semiconductor elements is mounted, for example, as described in Patent Document 1, a metal of Al (aluminum) on a ceramic substrate made of AlN (aluminum nitride). A power module substrate is used in which the plates are bonded via an Al—Si brazing material. This metal plate is used as a circuit layer, and a semiconductor element as a power element is mounted on the circuit layer via a solder material. It has been proposed that a metal plate such as Al is joined to the lower surface of the ceramic substrate to form a metal layer for heat dissipation, and a cooler is joined via the metal layer.
In such a power module substrate, heat generated from the semiconductor element is dissipated to the cooler via the circuit layer, the ceramic substrate, and the like.

Recently, power modules have become smaller and thinner, and the usage environment has become harsh, and the amount of heat generated from semiconductor elements tends to increase, and heat can be efficiently dissipated. There is a demand for a power module substrate that can be used. Further, as the output of the semiconductor element increases, a relatively large current may be passed through the circuit layer.
In view of this, a power module substrate has been proposed in which the thickness of the circuit layer is increased so as to exceed, for example, 0.6 mm. In this case, it is possible to promote heat dissipation by diffusing heat generated from the semiconductor element in the circuit layer in the direction of the plate surface of the power module substrate. That is, the circuit layer is used as a heat spreader. In addition, a large current can be applied by forming the circuit layer thick.

JP 2007-311528 A

  By the way, since the power module substrate described above has a structure in which a metal plate is laminated on a ceramic substrate, the thermal expansion coefficient of the entire power module substrate depends on the thickness of the ceramic substrate and the thickness of the metal plate. Will change. When the thickness of the ceramic substrate is relatively thick, the thermal expansion coefficient depends on the ceramic substrate and becomes relatively small. On the other hand, when the metal plate (circuit layer) is relatively thick, the thermal expansion coefficient depends on the metal plate and becomes relatively large.

Here, since the thermal expansion coefficient of silicon constituting the semiconductor element is as small as about 2 × 10 ⁻⁶ / ° C., in the power module substrate in which the circuit layer is formed thick as described above, the thermal expansion coefficient of the semiconductor element is And the thermal expansion coefficient of the power module substrate are greatly different. Then, when a thermal cycle is applied to a power module in which a semiconductor element is mounted on the power module substrate, the stress due to the difference in thermal expansion coefficient acts on the solder layer, and a crack is generated in the solder layer. There was a problem such as.

Thus, it is conceivable to suppress the occurrence of cracks in the solder layer by interposing a Mo plate or Cu—Mo plate having a thermal expansion coefficient close to that of the semiconductor element as a buffer layer between the circuit layer and the semiconductor element.
However, in Mo and Cu-Mo alloys, since the thermal conductivity is low, the heat generated from the semiconductor element cannot be sufficiently diffused toward the plate surface direction of the power module substrate, and the heat is dissipated. There was a problem that it was not possible to perform efficiently.

  The present invention has been made in view of the above-described circumstances, and can efficiently dissipate heat generated from a semiconductor element, and can be interposed between the semiconductor element even when a cooling cycle is applied. It is an object of the present invention to provide a power module substrate that can suppress generation of cracks in the mounted solder layer and that can constitute a power module that is excellent in reliability, and a power module that uses this power module substrate.

In order to solve such problems and achieve the above object, the power module substrate of the present invention has a circuit layer made of metal disposed on one surface of a ceramic substrate, and a semiconductor is formed on the circuit layer. A power module substrate on which an element is mounted , wherein the ceramic substrate is made of AlN, and a ratio of a thickness A of the circuit layer to a thickness C of the ceramic substrate is 1.6 ≦ A / C ≦ 5.7. A metal matrix composite plate made of a metal matrix composite material in which a carbonaceous member is filled with a metal is disposed on one surface of the circuit layer, and one surface side of the metal matrix composite plate In addition, a metal skin layer made of metal filled in the carbonaceous member in the metal matrix composite material is formed, and the carbon matrix member is filled in the metal matrix composite material on the other surface side of the metal matrix composite plate. Second metal slabs made of a tempered metal Emission layer is formed, it is characterized in that the semiconductor element through the metal matrix composite plate is mounted.

In the power module substrate having this configuration, a metal matrix composite plate made of a metal matrix composite material in which a metal is filled in a carbonaceous member is disposed on one surface of the circuit layer. Since the semiconductor element is mounted via the plate, the thermal expansion coefficient of the metal matrix composite plate on which the semiconductor element is mounted is set to be smaller than the thermal expansion coefficient of copper, aluminum, or the like. It is possible to suppress the occurrence of cracks in the solder layer due to the thermal cycle. That is, the metal matrix composite plate having a thermal expansion coefficient intermediate between the thermal expansion coefficient of the metal constituting the circuit layer and the thermal expansion coefficient of the semiconductor element alleviates the thermal stress and suppresses the occurrence of cracks in the solder layer. It becomes possible. Such an effect is particularly remarkable in a power module substrate having a circuit layer formed relatively thick.
In addition, since a metal skin layer made of a metal filled in a carbonaceous member in the metal matrix composite material is formed on one surface side of the metal matrix composite plate, the semiconductor element can be securely connected via the solder layer. Can be mounted on. Further, by performing Ni plating or the like on the metal skin layer, it is possible to further improve the adhesion to the solder material.
Furthermore, a second metal skin layer made of metal filled in a carbonaceous member in the metal matrix composite material is formed on the other surface side of the metal matrix composite plate. Accordingly, it is possible to satisfactorily bond the circuit layer made of metal and the metal matrix composite plate.

Here, it is preferable that the thermal expansion coefficient of the metal matrix composite plate is 8 × 10 ⁻⁶ / ° C. or less.
In this case, since the thermal expansion coefficient of the metal matrix composite plate is 8 × 10 ⁻⁶ / ° C. or less, the thermal expansion coefficient of the metal matrix composite plate on which the semiconductor element is mounted is equal to the thermal expansion coefficient of the semiconductor element. Thus, the generation of solder cracks can be reliably suppressed, and the reliability of the power module substrate can be greatly improved.

The metal matrix composite plate preferably has anisotropy so that the thermal conductivity in one direction is higher than the thermal conductivity in the other direction.
In this case, since it has anisotropy so that the thermal conductivity in one direction is higher than the thermal conductivity in the other direction, in the metal matrix composite plate, the heat generated from the semiconductor element is in one direction. It can be preferentially transmitted toward and can be designed to dissipate heat efficiently.

The thermal conductivity in the high thermal conductivity direction of the metal matrix composite plate is set to 400 W / m · K or more, and the thermal conductivity in the direction orthogonal to the high thermal conductivity direction is set to 200 W / m · K or more. It is preferable.
In this case, since the thermal conductivity in the high thermal conductivity direction is set to 400 W / m · K or more, the heat generated from the semiconductor element can be preferentially dissipated in the high thermal conductivity direction. In addition, since the thermal conductivity in the direction orthogonal to the high thermal conductivity direction is 200 W / m · K or more, heat is transferred also in directions other than the high thermal conductivity direction, and the heat generated from the semiconductor element. Can be efficiently diffused.

Furthermore, it is preferable that the high thermal conductivity direction is configured to face the thickness direction of the metal matrix composite plate.
In this case, since the high thermal conductivity direction in the metal matrix composite plate is configured to face the thickness direction of the metal matrix composite plate, heat generated from the semiconductor element is preferentially transmitted to the circuit layer. It is possible to dissipate heat efficiently by spreading heat in the direction of the plate surface of the power module substrate in the circuit layer.

Moreover, it is preferable that the metal material filled in the metal matrix composite material constituting the metal matrix composite plate is aluminum or an aluminum alloy.
In this case, since the melting point of aluminum or aluminum alloy is relatively low, the aluminum or aluminum alloy can be filled in the carbonaceous member relatively easily. Further, the thermal conductivity of the metal matrix composite plate in the high heat conduction direction is 400 to 450 W / m · K, the thermal expansion coefficient of RT to 200 ° C. is 6 to 8 × 10 ⁻⁶ / ° C., and the direction orthogonal to the high heat conduction direction. With a thermal conductivity of 200 to 250 W / m · K and RT to 200 ° C. of 2 to 4 × 10 ⁻⁶ / ° C., and cracking of the solder layer caused by the difference in thermal expansion coefficient with the semiconductor element Can be suppressed and heat can be efficiently dissipated.

Or it is preferable that the metal material with which the metal matrix composite material which comprises the said metal matrix composite board is filled is copper or a copper alloy.
In this case, the thermal conductivity of the metal matrix composite plate is 500 to 650 W / m · K, the thermal expansion coefficient is 5 to 7 × 10 ⁻⁶ / ° C., and the solder layer of the solder layer due to the difference in thermal expansion coefficient with the semiconductor element Generation of cracks can be suppressed and heat can be efficiently dissipated.

A power module according to the present invention includes the power module substrate described above and a semiconductor element mounted on one surface side of the metal matrix composite plate of the power module substrate.
According to the power module having this configuration, the heat generated from the semiconductor element can be efficiently dissipated, and cracks are not generated in the solder layer even during a cold cycle load. Therefore, the reliability of the power module can be greatly improved.

  According to the present invention, it is possible to efficiently dissipate heat generated from a semiconductor element, and suppress the generation of cracks in a solder layer interposed between the semiconductor element even when a cooling cycle is applied. It is possible to provide a power module substrate capable of configuring a power module with excellent reliability and a power module using the power module substrate.

It is a schematic explanatory drawing of the board | substrate for power modules which is embodiment of this invention, and a power module. FIG. 2 is an enlarged explanatory view of a metal matrix composite plate and a circuit layer of the power module substrate shown in FIG. 1. It is a flowchart of the manufacturing method of the power module shown in FIG. It is explanatory drawing of the manufacturing method of a metal matrix composite board. It is a schematic explanatory drawing of the board | substrate for power modules which is a reference form of this invention, and a power module. FIG. 6 is an enlarged explanatory view of a metal matrix composite plate and a circuit layer of the power module substrate shown in FIG. 5. It is a flowchart of the manufacturing method of the power module shown in FIG.

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 show a power module substrate 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, and a semiconductor element bonded to one surface (upper surface in FIG. 1) of the power module substrate 10 via a solder layer 2. 3 and a cooler 30 disposed on the other surface (the lower surface in FIG. 1) side of the power module substrate 10.

The semiconductor chip 3 is made of Si and has a thermal expansion coefficient of about 2 to 3 × 10 ⁻⁶ / ° C. The semiconductor chip 3 is bonded via a solder layer 2 made of, for example, a Sn—Ag, Sn—In, or Sn—Ag—Cu solder material.

  The cooler 30 is for cooling the power module substrate 10 described above, and has a multi-hole tube structure provided with a plurality of flow paths 31 for circulating a cooling medium (for example, cooling water). The cooler 30 is preferably made of a material having good thermal conductivity, and is made of A6063 (aluminum alloy) in the present embodiment.

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). Further, the thickness C of the ceramic substrate 11 is set within a range of 0.2 mm or more and 1.5 mm or less, and is set to 0.635 mm in the present embodiment. In the present embodiment, as shown in FIG. 1, the width of the ceramic substrate 11 is set wider than the widths of the circuit layer 12 and the metal layer 13.

The circuit layer 12 is formed by bonding a conductive metal plate to one surface of the ceramic substrate 11. In the present embodiment, the circuit layer 12 is formed by joining a metal plate made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more to the ceramic substrate 11.
Here, the thickness A of the circuit layer 12 is set in a range of 0.6 mm or more and 3.6 mm or less, and in this embodiment, A = 1.0 mm. Further, the ratio A / C between the thickness A of the circuit layer 12 and the thickness C of the ceramic substrate 11 is set within a range of 1.5 ≦ A / C ≦ 12. That is, in the present embodiment, the circuit layer 12 is formed to be relatively thick.

The metal layer 13 is formed by bonding a metal plate to the other surface of the ceramic substrate 11. In the present embodiment, the metal layer 13 is formed by joining a metal plate 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. Has been.
The thickness of the metal layer 13 is set within a range of 0.25 mm to 3.6 mm, and is set to 0.6 mm in the present embodiment.

On the upper surface of the circuit layer 12, a metal matrix composite plate 20 made of a metal matrix composite material in which a metal is filled in a carbonaceous member is disposed.
A first metal skin layer 21 made of metal filled in a carbonaceous member is formed on one surface of the metal matrix composite plate 20. An Ni plating layer 5 is formed on the first metal skin layer 21, and the semiconductor chip 3 is mounted on the Ni plating layer 5 via the solder layer 2.
Furthermore, a second metal skin layer 22 made of metal filled in the carbonaceous member is formed on the other surface of the metal matrix composite plate 20.

In the present embodiment, the metal based composite material constituting the metal matrix composite plate 20, in a carbonaceous member that is the average spacing d ₀₀₂ is 0.340nm or less, a purity of 99% or more of aluminum (pure aluminum) 90% by volume or more of the pores of the carbonaceous member is replaced with pure aluminum, and the content of pure aluminum is 35% based on the total volume of the aluminum-graphite composite material. It is as follows.
The first metal skin layer 21 and the second metal skin layer 22 described above are made of aluminum (pure aluminum) with a purity of 99% or more filled in the carbonaceous member.

  Here, the above-mentioned carbonaceous member is manufactured by extrusion processing, and is configured such that carbon crystals are arranged along the extrusion direction. Therefore, when the carbonaceous member is filled with aluminum, the aluminum is continuously disposed in the extrusion direction of the carbonaceous member, and the thermal conductivity is increased. On the other hand, in the direction crossing the extrusion direction, aluminum is divided by the carbonaceous member, and the thermal conductivity is lowered. Thus, the aluminum-graphite composite material (metal matrix composite material) constituting the metal matrix composite plate 20 has a higher thermal conductivity in the extrusion direction of the carbonaceous member than the thermal conductivity in the other directions. It has anisotropy, and the extrusion direction of the carbonaceous member is the high thermal conductivity direction.

In this embodiment, the thermal expansion coefficient of the metal matrix composite plate 20 is 8 × 10 ⁻⁶ / ° C. or less. Further, the thermal conductivity in the high thermal conductivity direction of the metal matrix composite plate 20 is 400 W / m · K or more, specifically, 400 to 450 W / m · K, and the direction orthogonal to the high thermal conductivity direction. The thermal conductivity is 200 W / m · K or more, specifically 200 to 250 W / m · K.

  Further, the thickness D of the metal matrix composite plate 20 is set within a range of 0.5 mm or more and 3 mm or less, and in this embodiment, D = 1.2 mm. The thickness E of the first skin layer 21 is set in the range of 0.05 mm or more and 0.8 mm or less, and in this embodiment, E = 0.2 mm. The thickness F of the second metal skin layer 22 is set within a range of 0.05 mm or more and 0.8 mm or less, and in the present embodiment, F is set to 0.2 mm.

Next, the manufacturing method of the power module 1 which is this embodiment is demonstrated with reference to FIG.3 and FIG.4.
First, the metal matrix composite plate 20 made of an aluminum-graphite composite material is formed (metal matrix composite plate forming step S1). This metal matrix composite plate forming step S1 will be described with reference to FIG. First, a graphite plate 41 having a porosity of 10 to 30% by volume is prepared. At this time, the extrusion direction in the graphite plate 41 (carbonaceous member) shall be in the thickness direction. Holding plates 42 and 42 made of graphite having a porosity of 5% by volume or less are disposed on both surfaces of the graphite plate 41, and the holding plates 42 and 42 and the graphite plate 41 are pressed by stainless pressing plates 43 and 43. Hold it. This is heated to 750 to 850 ° C. under a pressure of, for example, 100 to 200 MPa, impregnated with molten aluminum having a purity of 99.98% or more into the graphite plate 41, cooled and solidified, and the aluminum-graphite composite material is used. A metal matrix composite plate 20 is produced. At this time, a part of the molten aluminum oozes out on the surface of the graphite plate 41 (metal matrix composite plate 20) to form aluminum layers 44 and 44. The first metal skin layer 21 and the second skin layer 22 are formed by cutting the aluminum layers 44 and 44 to adjust the thickness.

  Next, an aluminum plate to be the circuit layer 12 and an aluminum plate to be the metal layer 13 are prepared, and these aluminum plates are laminated on one surface and the other surface of the ceramic substrate 11 through brazing materials, respectively, The aluminum plate and the ceramic substrate 11 are joined by cooling after pressing and heating (metal plate joining step S2). In this metal plate joining step S2, for example, an Al—Si alloy foil is used as the brazing material, and the brazing temperature is set to 600 ° C. to 640 ° C.

Next, the metal matrix composite plate 20 is bonded onto the circuit layer 12 (metal matrix composite plate bonding step S3). Here, since the second metal skin layer 22 made of aluminum is formed on the other surface side of the metal matrix composite plate 20, the second metal skin layer 22 and the circuit layer 12 are joined. become. In the metal matrix composite plate joining step S3, the second metal skin layer 22 and the circuit layer 12 are joined via an Al—Si brazing material, and the brazing temperature is set to 580 ° C. to 620 ° C. Has been.
In this way, the power module substrate 10 according to the present embodiment is produced. The metal plate joining step S2 and the metal matrix composite plate joining step S3 can be performed simultaneously.

Next, the cooler 30 is joined to the other surface side of the power module substrate 10 (cooler joining step S4). In this cooler joining step S4, the metal layer 13 and the cooler 30 are joined via an Al—Si brazing material, and the brazing temperature is set to 580 ° C. to 620 ° C. .
Next, the Ni plating film 5 is formed on the surface of the first metal skin layer 21 formed on one surface side of the metal matrix composite plate 20 (Ni plating step S5). In this Ni plating step S5, any method of electrolytic plating or electroless plating can be used.

Then, the semiconductor chip 3 is placed on the Ni plating film 5 formed on one surface side of the metal matrix composite plate 20 via a solder material, and soldered in a reduction furnace (semiconductor element bonding step S6). ).
As a result, the semiconductor chip 3 is bonded onto the power module substrate 10 via the solder layer 2, and the power module 1 according to this embodiment is produced.

In the power module substrate 10 and the power module 1 according to the present embodiment configured as described above, one surface of the circuit layer 12 is made of a metal matrix composite material in which a carbonaceous member is filled with a metal. Since the metal matrix composite plate 20 is disposed and the semiconductor chip 3 is mounted via the metal matrix composite plate 20, the coefficient of thermal expansion of the metal matrix composite plate 20 is 8 × 10 ⁻⁶ / ° C. or less. Thus, the thermal expansion coefficient of Si or the like constituting the semiconductor chip 3 is approximated, and the occurrence of cracks in the solder layer 2 due to the thermal cycle can be suppressed.

  Further, the metal matrix composite plate 20 has anisotropy so that the thermal conductivity in one direction is higher than the thermal conductivity in the other direction, and the high thermal conductivity direction in the metal matrix composite plate 20 is the metal Since it is configured to face the thickness direction of the base composite plate 20, heat generated from the semiconductor chip 3 can be preferentially transferred to the circuit layer 12, and in the circuit layer 12 formed relatively thick, Heat can be spread in the direction of the plate surface of the power module substrate 10, and heat can be efficiently dissipated.

  In the present embodiment, the thermal conductivity in the direction of high thermal conductivity in the metal matrix composite plate 20 is 400 W / m · K or more, specifically, 400 to 450 W / m · K. It is possible to dissipate the heat preferentially toward the high thermal conductivity direction (thickness direction of the metal matrix composite plate 20), and heat can be efficiently transferred to the circuit layer 12. Further, in the metal matrix composite plate 20, the thermal conductivity in the direction orthogonal to the high thermal conductivity direction is 200 W / m · K or more, specifically 200 to 250 W / m · K. Also in the board 20, heat is diffused in the direction of the board surface, and the heat generated from the semiconductor chip 3 can be efficiently dissipated.

In addition, since the metal material filled in the metal matrix composite material constituting the metal matrix composite plate 20 is aluminum which is a metal having a relatively low melting point, the carbonaceous member is relatively easily filled with aluminum. be able to. Further, as described above, the thermal conductivity of the metal matrix composite plate 20 in the high heat conduction direction is 400 to 450 W / m · K, and the thermal expansion coefficient of RT to 200 ° C. is 6 to 8 × 10 ⁻⁶ / ° C. The thermal conductivity in the direction orthogonal to the conduction direction is 200 to 250 W / m · K, the thermal expansion coefficient of RT to 200 ° C. is 2 to 4 × 10 ⁻⁶ / ° C., and the difference in thermal expansion coefficient with the semiconductor chip 3 is The occurrence of cracks in the solder layer 2 can be suppressed, and heat can be efficiently dissipated.

  In addition, since the first metal skin layer 21 made of aluminum filled in the carbonaceous member in the metal matrix composite material is formed on one surface of the metal matrix composite plate 20, the first metal skin layer 21 is formed. By forming the Ni plating film 5 on the semiconductor chip 3, the semiconductor chip 3 can be reliably mounted via the solder layer 2.

  Further, since the second metal skin layer 22 made of aluminum filled in the carbonaceous member in the metal matrix composite material is formed on the other surface side of the metal matrix composite plate 20, the second metal skin layer 22 is Accordingly, the circuit layer 12 made of aluminum and the metal matrix composite plate 20 can be bonded to each other via a brazing material.

In the present embodiment, the circuit layer 12 is made of aluminum, the thickness A of the circuit layer 12 is 0.6 mm or more, the thickness A of the circuit layer 12 and the thickness C of the ceramic substrate 11 Is set to 1.5 or more, the coefficient of thermal expansion of the portion below the metal matrix composite plate 20 approximates to the circuit layer 12 side, and the thermal stress caused by the metal matrix composite plate 20 is The effect of mitigation can be surely achieved.
On the other hand, since the thickness A of the circuit layer 12 is 3.6 mm or less and the ratio A / C between the thickness A of the circuit layer 12 and the thickness C of the ceramic substrate 11 is 12 or less, the cooling cycle load In some cases, it is possible to prevent peeling of the bonding interface, cracking of the ceramic substrate 11, and the like.

  As described above, according to the power module substrate 10 and the power module 1 of the present embodiment, the heat generated from the semiconductor chip 3 can be efficiently dissipated and the semiconductor chip can be loaded even when a cooling cycle is applied. Generation of cracks in the solder layer 2 interposed between the power module 3 and the power module substrate 10 and the power module 1 can be improved.

Next, a reference embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 5, the power module 101 of this reference form is bonded to the power module substrate 110 and one surface (the upper surface in FIG. 5) side of the power module substrate 110 via a solder layer 102. The semiconductor chip 103 and the cooler 130 disposed on the other surface (the lower surface in FIG. 5) side of the power module substrate 110 are provided. Here, the solder layer 102 is made of, for example, Sn—Ag, Sn—In, or Sn—Ag—Cu solder.

The cooler 130 is for cooling the power module substrate 110 described above,
A top plate portion 131 and heat radiating fins 132 suspended from the top plate portion 131 are provided. The cooler 130 is preferably made of a material having good thermal conductivity. In the present embodiment, the cooler 130 is made of, for example, copper such as oxygen-free copper or a copper alloy.

The power module substrate 110 includes a ceramic substrate 111, a circuit layer 112 disposed on one surface (the upper surface in FIG. 5) of the ceramic substrate 111, and the other surface (the lower surface in FIG. 5) of the ceramic substrate 111. And a disposed metal layer 113.
The ceramic substrate 111 prevents electrical connection between the circuit layer 112 and the metal layer 113, and is made of highly insulating Si ₃ N ₄ (silicon nitride). Further, the thickness C of the ceramic substrate 111 is set within a range of 0.2 mm or more and 1.5 mm or less, and is set to 0.32 mm in the present embodiment. In the present embodiment, as shown in FIG. 5, the width of the ceramic substrate 111 is set wider than the widths of the circuit layer 112 and the metal layer 113.

The circuit layer 112 is formed by bonding a conductive metal plate to one surface of the ceramic substrate 111. In the present embodiment, the circuit layer 112 is formed by bonding a metal plate made of a pure copper rolled plate having a purity of 99.999% or more to the ceramic substrate 111.
Here, the thickness A of the circuit layer 112 is set in a range of 0.6 mm or more and 3.6 mm or less, and in this embodiment, A = 1.0 mm. The ratio A / C between the thickness A of the circuit layer 112 and the thickness C of the ceramic substrate 111 is set in a range of 1.5 ≦ A / C ≦ 12. That is, in the present embodiment, the thickness of the circuit layer 112 is relatively thick.

The metal layer 113 is formed by bonding a metal plate to the other surface of the ceramic substrate 111. In the present embodiment, the metal layer 113 is formed by bonding a metal plate made of a pure copper rolled plate having a purity of 99.999% or more to the ceramic substrate 111, similarly to the circuit layer 112.
The thickness of the metal layer 113 is set within a range of 0.25 mm to 3.6 mm, and is set to 0.6 mm in the present embodiment.

A metal matrix composite plate 120 made of a metal matrix composite material in which a carbonaceous member is filled with metal is disposed on the upper surface of the circuit layer 112.
A first metal skin layer 121 made of a metal filled in a carbonaceous member is formed on one surface of the metal matrix composite plate 120, and the upper solder layer 102 of the first metal skin layer 121 is formed. The semiconductor chip 103 is mounted via
Further, a second metal skin layer 122 made of metal filled in the carbonaceous member is formed on the other surface of the metal matrix composite plate 120.

In the present embodiment, the metal matrix composite material constituting the metal matrix composite plate 120 is composed of a copper-graphite composite material in which a pure carbon having a purity of 99% or more is filled in a carbonaceous member. 90% by volume or more of the pores are replaced by pure copper, and the pure copper content is 35% or less based on the total volume of the copper-graphite composite material.
Further, the first metal skin layer 121 and the second metal skin layer 122 described above are made of pure copper with a purity of 99% or more filled in the carbonaceous member.

Here, the aforementioned metal matrix composite plate 120 has anisotropy so that the thermal conductivity in the extrusion direction of the carbonaceous member is higher than the thermal conductivity in the other direction, The extrusion direction is the high thermal conductivity direction.
In the present embodiment, the thermal conductivity in the high thermal conductivity direction of the metal matrix composite plate 120 is 500 W / m · K or more, specifically 500 to 550 W / m · K, and in this high thermal conductivity direction. The thermal conductivity in the orthogonal direction is 300 W / m · K or more, specifically, 300 to 350 W / m · K.
Moreover, the thermal expansion coefficient of the metal matrix composite plate 120 is 8 × 10 ⁻⁶ / ° C. or less.

  In addition, the thickness D of the metal matrix composite plate 120 is set within a range of 0.5 mm or more and 3 mm or less, and in this embodiment, D = 1.2 mm. The thickness E of the first skin layer 121 is set in the range of 0.05 mm or more and 0.8 mm or less, and in this embodiment, E = 0.2 mm. The thickness F of the second skin layer 122 is set in a range of 0.05 mm or more and 0.8 mm or less, and in this embodiment, F is set to 0.2 mm.

Next, the manufacturing method of the power module 101 which is this embodiment is demonstrated with reference to FIG.
First, the metal matrix composite plate 120 made of a copper-graphite composite material is formed (metal matrix composite plate forming step S11). In this metal matrix composite plate forming step S11, a graphite plate having a porosity of 10 to 30% by volume is sandwiched between a pair of sandwich plates made of graphite having a porosity of 5% by volume or less and a pair of pressing plates made of stainless steel. For example, a metal matrix composite plate made of a copper-graphite composite material is heated to 750 to 850 ° C. under a pressure of 100 to 200 MPa, impregnated with a molten copper having a purity of 99% or more, and cooled and solidified. 120 is produced. At this time, a part of the molten copper oozes out on the surface of the graphite plate (metal matrix composite plate 120) to form a copper layer. By cutting the copper layer and adjusting the thickness, the first metal skin layer 121 and the second skin layer 122 are formed.

  Next, a copper plate to be the circuit layer 112 and a copper plate to be the metal layer 113 are prepared, and these copper plates are laminated on one surface and the other surface of the ceramic substrate 111 through brazing materials, respectively, and pressed and heated. The copper plate and the ceramic substrate 111 are joined by post-cooling (metal plate joining step S12). In this metal plate joining step S12, joining is performed via an Ag—Cu brazing material, and the brazing temperature is set to 800 ° C. to 900 ° C.

Next, the metal matrix composite plate 120 is bonded onto the circuit layer 112 (metal matrix composite plate bonding step S13). Here, since the second metal skin layer 122 made of copper is formed on the other surface side of the metal matrix composite plate 120, the second metal skin layer 122 and the circuit layer 112 are joined. become. In the metal matrix composite plate joining step S13, the second metal skin layer 122 and the circuit layer 112 are joined via an Ag—Cu brazing material, and the brazing temperature is set to 800 ° C. to 870 ° C. Has been.
In this way, the power module substrate 110 according to the present embodiment is produced. In addition, it is also possible to perform metal plate joining process S12 and metal matrix composite board joining process S13 simultaneously.

  Next, the cooler 130 is joined to the other surface side of the power module substrate 110 (cooler joining step S14). In this cooler joining step S14, the metal layer 113 and the cooler 130 are joined via an Ag—Cu brazing material, and the brazing temperature is set to 800 ° C. to 870 ° C. .

Then, the semiconductor chip 103 is placed on one surface of the metal matrix composite plate 120 via a solder material and soldered in a reduction furnace (semiconductor element bonding step S15).
As a result, the semiconductor chip 103 is bonded onto the power module substrate 110 via the solder layer 102, and the power module 101 according to the present embodiment is produced.

In the insulating substrate 110 and the power module 101 which are reference forms configured as described above, the metal material filled in the metal matrix composite material constituting the metal matrix composite plate 120 is copper. The thermal conductivity in the direction perpendicular to the surface of the base composite plate 120 is 500 to 550 W / m · K, the thermal expansion coefficient in the direction parallel to the surface is 6 to 8 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient with the semiconductor chip 103 It is possible to suppress the occurrence of cracks in the solder layer 102 due to the difference between them and to efficiently dissipate heat.

  Further, since the metal material filled in the metal matrix composite material constituting the metal matrix composite plate 120 is copper and the circuit layer 112 is also composed of copper, the circuit layer 112 and the metal matrix composite plate 120 are connected to each other. It can be joined via a material.

  Further, since the first metal skin layer 121 made of copper is formed on one surface of the substrate body 120, the semiconductor chip 103 can be bonded via the solder material without forming the Ni plating film. . Therefore, the manufacturing cost of the power module 101 can be reduced.

In the present embodiment, the circuit layer 112 is made of copper, the thickness A of the circuit layer 112 is 0.6 mm or more, the thickness A of the circuit layer 112 and the thickness C of the ceramic substrate 11 Is set to 1.5 or more, the thermal expansion coefficient of the portion below the metal matrix composite plate 120 approximates to the circuit layer 112 side, and the thermal stress caused by the metal matrix composite plate 120 is The effect of mitigation can be surely achieved.
On the other hand, the thickness A of the circuit layer 112 is 3.6 mm or less, and the ratio A / C between the thickness A of the circuit layer 112 and the thickness C of the ceramic substrate 11 is 12 or less. Sometimes, it is possible to prevent peeling of the bonding interface, cracking of the ceramic substrate 111, and the like.

Next, the result of a confirmation experiment conducted to confirm the effect of the present invention will be described.
A carbonaceous member produced by the extrusion method was cut so that the extrusion direction was the thickness direction, and a graphite material was prepared. These were set in a mold, and after pouring a pure aluminum or pure copper melt, a metal matrix composite plate (aluminum-graphite composite material or copper-graphite composite material) was produced by applying high pressure.

The thermal conductivity of the thus produced aluminum-graphite composite material was measured by a laser flash method in a direction parallel to and perpendicular to the plate thickness direction. As a result, the thickness was 422 W / m · K in the thickness direction and 241 W / m · K in the vertical direction. Moreover, it was 7.1 * 10 < ^-6 > / degreeC as a result of measuring the average thermal expansion coefficient to RT-200 degreeC in a parallel direction in the surface.
Further, the thermal conductivity of the copper-graphite composite material was measured in a direction parallel to and perpendicular to the plate thickness direction by a laser flash method. As a result, the thickness was 530 W / m · K in the thickness direction and 342 W / m · K in the vertical direction. Moreover, it was 7.5 * 10 < ^-6 > / degreeC as a result of measuring the average thermal expansion coefficient to RT-200 degreeC in a parallel direction in the surface.
Using this metal matrix composite plate (aluminum-graphite composite material or copper-graphite composite material), the average thermal expansion coefficient, thermal resistance, solder cracks, and fracture at the interface between the metal plate and the ceramic substrate were evaluated.

First, a composite substrate in which a 50 mm square metal matrix composite plate and a metal plate were joined via a brazing material was prepared, the thermal expansion coefficient of the composite substrate was measured at RT to 200 ° C., and the average thermal expansion coefficient was calculated. .
Next, the thermal resistance Rth is obtained by bonding a 10 mm square silicon chip to the 50 mm square composite substrate via a solder material made of Sn-Ag-Cu, and heating the silicon chip to measure the temperature. The thermal resistance of the upper surface of the substrate and the lower surface of the metal plate was calculated by the following formula.
Rth = (Tj−Ta) / Q
Tj: silicon chip temperature, Ta: temperature of the lower surface of the composite substrate, Q (W): semiconductor chip heat generation

For solder cracks, the thermal resistance measurement sample described above was subjected to a temperature cycle of −40 ° C. to 125 ° C. × 3000 times (liquid phase), and then the cross section of the solder part under the silicon chip was observed to evaluate the degree of progress of the cracks (○ : Crack growth length from the end portion is 0.5 mm or less, Δ: Crack growth length from the end portion exceeds 0.5 mm, but there is no practical problem).
Regarding the fracture of the interface between the metal plate and the ceramic substrate, the sample for thermal resistance measurement described above was subjected to a temperature cycle of −40 ° C. to 125 ° C. × 3000 times (liquid phase), and then the cross section of the interface between the metal plate and the ceramic substrate was observed. The presence or absence of cracks in the ceramic substrate and the peeling of the interface was confirmed (◯: the crack progress length from the end portion was 1 mm or less, x: the crack progress length from the end portion was more than 1 mm).
The evaluation results are shown in Tables 1 and 2.

In Examples 1-20 and 25 provided with a metal matrix composite plate made of an aluminum-graphite composite material and a metal plate made of aluminum, no fracture at the interface between the metal plate and the ceramic substrate was observed. However, in Example 25 in which the ratio A / C between the thickness C of the ceramic substrate and the thickness A of the metal plate was 12, occurrence of solder cracks was observed.
In Examples 21-24 including a metal matrix composite plate made of a copper-graphite composite material and a metal plate made of copper, no fracture at the interface between the metal plate and the ceramic substrate was observed.

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 matrix composite material has been described as an aluminum-graphite composite material in which a carbonaceous member is filled with aluminum, or a copper-graphite composite material in which a carbonaceous member is filled with copper, but the present invention is not limited to this. Instead, it may be filled with an aluminum alloy, a copper alloy, or another metal.

Further, the carbonaceous member has been described as using a graphite plate (graphite member), but the carbonaceous member is not limited to this, and even a carbonaceous member made of silicon carbide (SiC), diamond, or the like. Good.
Furthermore, although the first metal skin layer and the second metal skin layer have been described as being formed by leaching aluminum or copper filled in the metal matrix composite plate, the present invention is not limited to this, When the base composite plate is formed, the first metal skin layer and the second metal skin layer may be formed by sandwiching an aluminum or copper plate material between the sandwich plates.

Furthermore, the structure and material of the cooler are not limited to the present embodiment, and other structures and materials may be used.
Moreover, although demonstrated by the structure which joined the cooler and the metal layer, you may interpose a buffer layer between a cooler and a metal layer.

DESCRIPTION OF SYMBOLS 1,101 Power module 2,102 Solder layer 3,103 Semiconductor chip (semiconductor element)
10, 110 Power module substrate 11, 111 Ceramic substrate 12, 112 Circuit layer 20, 120 Metal matrix composite plate 21, 121 First metal skin layer (metal skin layer)
22, 122 Second metal skin layer

Claims (8)

A power module substrate in which a circuit layer made of metal is disposed on one surface of a ceramic substrate, and a semiconductor element is mounted on the circuit layer,
The ceramic substrate is made of AlN, and the ratio of the thickness A of the circuit layer and the thickness C of the ceramic substrate is 1.6 ≦ A / C ≦ 5.7,
On one surface of the circuit layer, a metal matrix composite plate made of a metal matrix composite material filled with metal in a carbonaceous member is disposed,
A metal skin layer made of metal filled in a carbonaceous member in the metal matrix composite material is formed on one surface side of the metal matrix composite plate, and the metal matrix layer is formed on the other surface side of the metal matrix composite plate. A second metal skin layer made of metal filled in the carbonaceous member in the matrix composite material is formed;
A power module substrate on which a semiconductor element is mounted via the metal matrix composite plate. 2. The power module substrate according to claim 1, wherein a thermal expansion coefficient of the metal matrix composite plate is 8 × 10 ⁻⁶ / ° C. or less.   The power according to claim 1 or 2, wherein the metal matrix composite plate has anisotropy so that the thermal conductivity in one direction is higher than the thermal conductivity in the other direction. Module board.   The thermal conductivity in the high thermal conductivity direction of the metal matrix composite plate is 400 W / m · K or more, and the thermal conductivity in the direction perpendicular to the high thermal conductivity direction is 200 W / m · K or more. The power module substrate according to claim 3.   5. The power module substrate according to claim 3, wherein the high thermal conductivity direction is configured to face a thickness direction of the metal matrix composite plate.   6. The power module according to claim 1, wherein the metal material filled in the metal matrix composite material constituting the metal matrix composite plate is aluminum or an aluminum alloy. substrate.   6. The power module according to claim 1, wherein the metal material filled in the metal matrix composite material constituting the metal matrix composite plate is copper or a copper alloy. substrate. A power module substrate according to any one of claims 1 to 7 and a semiconductor element mounted on one surface side of the metal matrix composite plate of the power module substrate. A featured power module.

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