Heat transfer member and module with the same

A heat transfer member is disposed between a semiconductor element and an electrode plate. The heat transfer member comprises a metal portion extending between a first face at the semiconductor element side and a second face at the plate electrode side, and a ceramic portion surrounding the metal portion. An area of the first face is less than an area of the second face in the metal portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2012-126705 filed on Jun. 4, 2012, the contents of which are hereby incorporated by reference into the present application.

1. Technical Field

The technique disclosed in the specification relates to a heat transfer member disposed between a semiconductor element and an electrode plate. Further, the technique disclosed in the specification relates to a module with the heat transfer member.

2. Description of Related Art

There has been developed a module for radiating heat generated in a semiconductor element from both surfaces of the semiconductor element. In the module of this type, a cooler, an insulating substrate, a semiconductor element, a heat transfer member, and an electrode plate are laminated in this order. In the module of this type, heat generated in the semiconductor element is radiated from a rear surface of the semiconductor element via the insulating substrate and the cooler and also radiated from a front surface of the semiconductor element via the heat transfer member and the electrode plate.

Characteristics of the heat transfer member are desired to include both low electric resistance and quick radiation of the heat generated in the semiconductor element. Therefore, as a material of the heat transfer member, metal having a small resistance value and large thermal conductivity is used. In general, a coefficient of linear expansion of metal is larger than a coefficient of linear expansion of a semiconductor. Therefore, a larger difference in the coefficient of linear expansion is present between the semiconductor element and the heat transfer member. As a result, in the module of this type, deterioration in reliability such as a joining failure of the semiconductor element and the heat transfer member is caused by thermal strain that occurs because of a thermal expansion difference between the semiconductor element and the heat transfer member.

Japanese Patent Application Publication No. 2010-268011 discloses an example of a technique for relaxing such thermal strain. A heat transfer member described in the patent document 1 includes a metal portion and a ceramic portion surrounding the metal portion. With the technique, since the ceramic portion suppresses thermal expansion of the metal portion, a thermal expansion difference between a semiconductor element and the heat transfer member is reduced and thermal strain that occurs between the semiconductor element and the heat transfer member is relaxed.

In the heat transfer member disclosed in Japanese Patent Application Publication No. 2010-268011, in order to further reduce the thermal strain that occurs between the semiconductor element and the heat transfer member, it is desirable to reduce an area of the metal portion on a surface joined to the semiconductor element. However, the heat transfer member described in Japanese Patent Application Publication No. 2010-268011 has a form in which the metal portion and the ceramic portion respectively extend in parallel to a vertical direction. Therefore, when the area of the metal portion on the surface joined to the semiconductor element is reduced, a volume of the metal portion is also reduced and a heat radiation effect is deteriorated.

It is an object of a technique disclosed in this specification to provide a heat transfer member having a high heat radiation effect while suppressing a thermal expansion difference between the heat transfer member and a semiconductor element.

BRIEF SUMMARY OF INVENTION

A heat transfer member disclosed in this specification is to be disposed between a semiconductor element and an electrode plate. The heat transfer member includes a metal portion and a ceramic portion. The metal portion extends between a first face on the semiconductor element side and a second face on the electrode plate side. The ceramic portion surrounds the metal portion. In the metal portion, an area of the first face is less than an area of the second face.

In the heat transfer member in the aspect explained above, the area of the metal portion is relatively small on the first face on the semiconductor element side and the area of the metal portion is relatively large on the second face on the electrode plate side. Therefore, since an opposing area of the metal portion and the semiconductor element is small, thermal strain due to a thermal expansion difference between the metal portion and the semiconductor element is suppressed. On the other hand, since an opposing area of the metal portion and the electrode plate is large, an effect of radiating heat generated in the semiconductor element to the electrode plate via the metal portion is high.

A module disclosed in this specification includes a cooler, an insulating substrate disposed on the cooler, a semiconductor element disposed on the insulating substrate, a heat transfer member disposed on the semiconductor element, and an electrode plate disposed on the heat transfer member. The heat transfer member includes a metal portion extending between a first face on the semiconductor element side and a second face on the electrode plate side and a ceramic portion surrounding the metal portion. In the metal portion, an area of the first face is less than an area of the second face.

DETAILED DESCRIPTION OF INVENTION

Technical features disclosed in this specification are summarized below. Note that matters described below respectively independently have technical utility.

(Feature 1) A heat transfer member disclosed in this specification is disposed between a semiconductor element and an electrode plate. A semiconductor material of the semiconductor element is not specifically limited. In an example, as a material of the semiconductor element, a silicon, silicon carbide, or gallium nitride material may be used. A type of the semiconductor element is not specifically limited either. In an example, as the type of the semiconductor element, a MOSFET, an IGBT, a diode, a thyristor, an HFET, or an HEMT may be used. The semiconductor element may be either a vertical type or a horizontal type. The electrode plate is a conductor member for an electric current, which flows through the semiconductor element, to be input or output. In an example, the electrode plate may be a conductor member electrically connected to a front surface electrode of the vertical-type semiconductor element or may be a conductor member electrically connected to a rear surface electrode of the vertical-type semiconductor element.

(Feature 2) The heat transfer member disclosed in this specification may include a metal portion extending between a first face on the semiconductor element side and a second face on the electrode plate side and a ceramic portion surrounding the metal portion. The material of the metal portion is not specifically limited. A material of the metal portion is desirably a material having small electric resistance, small specific heat and large thermal conductivity. In an example, as the material of the metal portion, copper, aluminum, gold, or silver may be used. A material of the ceramic portion is not specifically limited either. The material of the ceramic portion is desirably a material having a Young's modulus higher than a Young's modulus of the material of the metal portion (equal to or higher than 120 MPa) and having a coefficient of linear expansion smaller than a coefficient of linear expansion of the material of the metal portion (equal to or smaller than 10 ppm/K). In an example, as the material of the ceramic portion, aluminum nitride (AlN), silicon nitride (Si3N4), alumina (Al2O3), or zirconium (ZrO3) may be used.

(Feature 3) In the metal portion, an area of the first face may be less than an area of the second face.

(Feature 4) In the metal portion, a first portion where an area of a cross section parallel to the first face and the second face is of a first value and a second portion where the area is of a second value may be present. The first value is smaller than the second value. In this case, the first portion may be located on the first face side and the second portion may be located on the second face side.

(Feature 5) The metal portion may be configured such that the area of the cross section parallel to the first face and the second face gradually increases from the first face to the second face.

(Feature 6) The metal portion may be formed integrally with the electrode plate. According to this aspect, since a joining surface is absent between the heat transfer member and the electrode plate, concentration of thermal strain between the heat transfer member and the electrode plate is relaxed. Note that, when the metal portion and the electrode plate are integrally molded, the second face in this specification refers to a cut surface between a portion perceivable as the metal portion and a portion perceivable as the electrode plate.

(Feature 7) The metal portion of the first face may be located above an element region of the semiconductor element. The element region of the semiconductor element is a region where a gate structure is formed. According to this aspect, heat generated in the semiconductor element is efficiently radiated via the metal portion. Further, the ceramic portion of the first face may be located above a termination region of the semiconductor element. The termination region of the semiconductor element is a region disposed around the element region and where the gate structure is not formed. For example, in the termination region of the semiconductor element, a guard ring, a resurf layer, and the like for withstand pressure improvement are formed. According to this aspect, capacity coupling between the metal portion and the termination region of the semiconductor element is suppressed and deterioration in withstand pressure of the termination region of the semiconductor element is suppressed.

Embodiment

InFIG. 1, a configuration of a vehicle-mounted power module1is shown. The power module1is used for an inverter device connected between a direct-current power supply and an alternating-current motor. The power module1has a structure in which a cooler10, an insulating substrate20, a semiconductor element30, a heat transfer member40, and an electrode plate50are laminated in this order.

The cooler10is a water cooling type and includes a plurality of through-holes through which cooling water flows. In an example, an Al—Mn aluminum alloy is used as a material of the cooler10.

The insulating substrate20is brazed on the cooler10via a brazing filler material and has a structure in which a metal layer22, an insulating layer24, and a wiring layer26are laminated. In an example, copper is used as a material of the metal layer22and the wiring layer26and aluminum nitride is used as a material of the insulating layer24.

The semiconductor element30is joined on the insulating substrate20via a solder material62. The semiconductor element30is made from silicon (Si) or silicon carbide (SiC) and is a power device of MOSFET or IGBT. In an example, an Sn—Cu or Sn—Ag—Cu material is used as a material of the solder material62.

The heat transfer member40is joined on the semiconductor element30via a solder material64. The heat transfer member40includes a metal portion42and a ceramic portion44. The metal portion42has a generally right cylindrical form and extends between a first face40A on a semiconductor element30side and a second face40B on an electrode plate50side. In an example, copper is used as a material of the metal portion42. The ceramic portion44has a generally cylindrical form and surrounds the metal portion42circulating around a side surface of the metal portion42. The ceramic portion44also extends between the first face40A on the semiconductor element30side and the second face40B on the electrode plate50side. In an example, aluminum nitride is used as a material of the ceramic portion44. The metal portion42and the ceramic portion44are joined by brazing or soldering.

The electrode plate50is disposed on the heat transfer member40and extends sideward from a top of the heat transfer member40. The electrode plate50is a metal plate having a tabular form. In an example, copper is used as a material of the electrode plate50. Note that both of the materials of the electrode plate50and the heat transfer member40are copper. The electrode plate50and the heat transfer member40are integrally molded.

The heat transfer member40is explained in detail. As shown inFIG. 2, when observed on a cross section parallel to the first face40A and the second face40B (corresponding to a cross section orthogonal to an up down direction on the paper surface), the generally right cylindrical metal portion42is configured by a first metal portion42ahaving a small sectional area and a second metal portion42bhaving a large sectional area. The first metal portion42ais located on the semiconductor element30side and joined to the semiconductor element30via solder64. The second metal portion42bis located on the electrode plate50side. When observed on the cross section parallel to the first face40A and the second face40B (the cross section orthogonal to the up down direction on the paper surface), the generally cylindrical ceramic portion44is configured by a first ceramic portion44ahaving a large sectional area and a second ceramic portion44bhaving a small sectional area. The first ceramic portion44ais located on the semiconductor element30side and surrounds the first metal portion42a. The first ceramic portion44ais joined to the semiconductor element30via the solder64. The second ceramic portion44bis located on the electrode plate50side and surrounds the second metal portion42b.

The first metal portion42aof the metal portion42is located above an element region (a region where a gate structure is disposed) of the semiconductor element30. The first ceramic portion44aof the ceramic portion44is located above a termination region (a region disposed around the element region and where the gate structure is not disposed) of the semiconductor element30.

The first face40A of the heat transfer member40is shown inFIG. 3. The second face40B of the heat transfer member40is shown inFIG. 4. The heat transfer member40is configured such that an area of the metal portion42(corresponding to the first metal portion42a) of the first face40A is relatively small and an area of the metal portion42(corresponding to the second metal portion42b) of the second face40B is relatively large. On the other hand, the heat transfer member40is configured such that an area of the ceramic portion44(corresponding to the first ceramic portion44a) of the first face40A is relatively large and an area of the ceramic portion44(corresponding to the second ceramic portion44b) of the second face40B is relatively small.

Characteristics of the power module1are explained. Silicon is used as the material of the semiconductor element30. A coefficient of linear explanation of the semiconductor element30is about 3. Copper is used as a material of the metal portion42of the heat transfer member40. A coefficient of linear expansion of the metal portion42is about 17. Aluminum nitride is used as a material of the ceramic portion44of the heat transfer member40. A coefficient of linear expansion of the ceramic portion44is 4. That is, a difference in the coefficient of linear expansion between the metal portion42of the heat transfer member40and the semiconductor element30is larger than a difference in the coefficient of linear expansion between the ceramic portion44of the heat transfer member40and the semiconductor element30.

In the heat transfer member40of the power module1, the ceramic portion44surrounds the metal portion42and thermal expansion of the metal portion42is suppressed. Therefore, the heat transfer member40as a whole has a coefficient of linear expansion depending on the ceramic portion44. Since the difference in the coefficient of thermal expansion between the ceramic portion44of the heat transfer member40and the semiconductor element30is small, thermal strain that occurs between the semiconductor element30and the heat transfer member40is suppressed.

Further, in the power module1, an area of the metal portion42on the first face40A of the heat transfer member40is small. Therefore, thermal strain that occurs between the semiconductor element30and the heat transfer member40is suppressed. On the other hand, an area of the metal portion42on the second face40B of the heat transfer member40is large. Therefore, heat generated in the semiconductor element30can be efficiently radiated to the electrode plate50. Further, since a volume of the metal portion42in the heat transfer member40is large, a heat capacity increases. Therefore, a sudden temperature rise of the heat transfer member40is suppressed.

Other characteristics of the power module1are explained below.

(1) In the power module1, the metal portion42of the heat transfer member40and the electrode plate50are integrally molded. Therefore, since a joining surface is absent between the metal portion42of the heat transfer member40and the electrode plate50, concentration of thermal strain between the metal portion42of the heat transfer member40and the electrode plate50is suppressed.

(2) As shown inFIG. 2, in the heat transfer member40, the metal portion42is located above the element region of the semiconductor element30and the ceramic portion44is located above the termination region of the semiconductor element30. In general, a temperature distribution in the semiconductor element30has a peak in a center of the element region. Since the metal portion42is located above the element region of the semiconductor element30, heat generated in the semiconductor element30can be efficiently radiated. Since the ceramic portion44is located above the termination region of the semiconductor element30, capacity coupling between the metal portion42and the termination region of the semiconductor element30is suppressed and withstand pressure of the termination region is maintained.

(3) Other examples of the first face40A of the heat transfer member40are shown inFIGS. 5 to 7. In general, a maximum value of thermal strain appears on a diagonal line having a maximum distance. Therefore, in order to suppress thermal strain, it is desirable to adopt a layout for reducing a length of the metal portion42arranged on the diagonal line. As shown inFIGS. 5 and 6, when observed in an arbitrary direction passing a center point P of the heat transfer member40, a layout in which a minimum value of (length of the metal portion42)/(length of the heat transfer member40) is on the diagonal line is desirable. As shown inFIG. 7, a layout in which the metal portion42is not arranged on the diagonal line is desirable.

(4) The power module1may include the heat transfer member40having a form shown inFIG. 8. When observed on the cross section parallel to the first face40A and the second face40B, the heat transfer member40in this example is configured such that a sectional area of the metal portion42gradually increases from the first face40A to the second face40B. The heat transfer member40in this example has effects same as the effects explained above.

(5) The power module1may include the heat transfer member40having a form shown inFIG. 9. The ceramic portion44of the heat transfer member40in this example includes a ceramic mesh portion41on the first face40A side. Therefore, the heat transfer member40has a characteristic in that, when observed on the cross section parallel to the first face40A and the second face40B, the metal portion42on the first face40A side is divided into a plurality of portions. For example, as shown inFIG. 10, the ceramic mesh portion41may be formed in a stripe shape. Alternatively, as shown inFIG. 11, the ceramic mesh portion41may be formed in a lattice shape. The heat transfer member40in these examples has effects same as the effects explained above. Further, in the heat transfer member40in these examples, since the metal portion42on the first face40A side is divided into a plurality of portions, thermal strain is suppressed from accumulating and increasing and is further relaxed.