JP2014207490A - Insulating substrate, process of manufacturing the same, semiconductor module, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve with a simple structure and at low cost insulation properties of an end face of a side face part in an insulating substrate provided with an isolating layer formed by spray coating a ceramic powder to one side surface of a conductive substrate.SOLUTION: A structure of a side face part of the insulating substrate is so configured that a creepage distance of insulation between a conductive base material and a metal member in a state where the metal member is brought in contact with and mounted to a surface of an insulating layer becomes larger than a thickness of the insulating layer.

Description

The present invention relates to an insulating substrate having an insulating layer formed on the surface of a conductive substrate, a method for manufacturing the same, a semiconductor module using the insulating substrate, and a semiconductor device.

(B) In recent years, power modules such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) that can operate in a large capacity and high voltage environment have been widely used in consumer and industrial equipment. It is used. Among various modules using these semiconductor elements (hereinafter referred to as “semiconductor modules”), there are various reasons such as when the power handled is large, the degree of circuit integration is high, or the circuit operating frequency is high. Therefore, there is a thing that must appropriately dissipate the heat generated by the mounted semiconductor element.
(B) FIG. 9 is a diagram showing the contents of Patent Document 1. The power semiconductor module shown in FIG. 9 includes a ceramic insulating substrate 51 in which a front circuit board 57 and a back circuit board 58, which are conductor layers, are formed on both surfaces of a ceramic substrate 53, respectively. A power semiconductor chip 55 is bonded to the surface circuit board 57 of the ceramic insulating substrate 51 via a solder layer 56. Further, a metal base 54 made of copper or a copper alloy is bonded via a solder layer 56 on the back circuit board 58 on the surface of the ceramic insulating substrate 51 opposite to the bonding surface with the power semiconductor chip 55. . Further, a cooling body (not shown) is bonded to the surface of the metal base 54 opposite to the bonding surface with the ceramic insulating substrate 53 via a thermal compound. (C) In such a conventional power semiconductor module structure, the members are complicated and the total cost for manufacturing is high.

  Therefore, for example, as disclosed in Patent Document 2, a power semiconductor module using an insulating substrate (conductive substrate with an insulating layer) provided with an insulating layer formed by directly spraying ceramic powder on a conductive substrate. It has been devised.

JP 2002-203942 A JP 2007-307772 A

(A) Applying an insulating substrate having an insulating layer formed by spraying ceramic powder on the surface of a conductive base material as shown in Patent Document 2, for example, a semiconductor module as shown in FIG. However, when a semiconductor device is configured by attaching a heat sink to such a semiconductor module, there is a problem in securing the insulating property of the end face of the insulating substrate.
(B) FIG. 10 is a cross-sectional view showing a different configuration example of the semiconductor module according to the prior art, and shows the configuration of the semiconductor module to which the above-described insulating substrate is applied. In the semiconductor module 21 shown in FIG. 10A, an insulating layer 7 formed by spraying ceramic powder on the first surface 1a of the conductive substrate 1 having the first surface 1a and the second surface 1b is provided. The provided insulating substrate 11 is provided. The semiconductor circuit elements 2 and 2 which are power semiconductor elements, such as IGBT, are joined to the 2nd surface 1b of the electroconductive base material 1, for example by solder, and the 2nd surface of the electroconductive base material 1 is directly or indirectly. It is mounted so as to contact the surface 1b. The connection terminals (not shown) of the semiconductor circuit elements 2 and 2 are electrically connected to the lead frame 6 by a bonding wire 4 made of an aluminum wire having a wire diameter of 125 to 500 μm, for example. Then, each of the above-described elements, that is, the insulating substrate 11, the semiconductor circuit elements 2 and 2, the lead frame 6, and the bonding wire 4, for example, a molding resin 5 for sealing made of an epoxy resin mixed with an inorganic filler. The semiconductor module 21 is configured by being sealed.

The semiconductor module 21 configured in this manner is sealed by covering all surfaces other than the first surface 1a of the conductive substrate 1 together with the semiconductor circuit elements 2 and 2 with the molding resin 5 which is an insulating material. ing. For this reason, except for the end 62 of the lead frame 6 for electrical connection, only the insulating layer 7 formed on the molding resin 5 and the first surface 1a is in contact with the outside world on the surface of the semiconductor module 21. That is, the surface of the semiconductor module 21 is an insulating surface that insulates the conductive substrate 1 from the outside. The semiconductor module 21 is attached in close contact with the heat sink 8 to constitute a semiconductor device 31.
(C) FIG. 10B is an enlarged cross-sectional view of a portion C in FIG. 10A, and shows an insulating structure near the end surface of the side surface of the insulating substrate 11 in a state where the semiconductor module 21 is attached in close contact with the heat sink 8. Is shown. In the insulating structure of FIG. 10B, the insulating creepage distance between the conductive substrate 1 and the heat sink 8 is the same as the thickness d of the insulating layer 7. Depending on the insulation specifications required for the semiconductor device 31, it is necessary to increase the insulation creepage distance between the conductive base material 1 and the heat sink 8 and improve the insulation of the side surface end face of the insulating substrate 11. .

In this regard, as a measure for enhancing the insulation of the side surface end face of the insulating substrate 11, for example, by increasing the thickness d of the insulating layer 7 formed on the first surface 1 a of the conductive member 1, It is conceivable to increase the distance. However, in this case, as the thickness d of the insulating layer 7 increases, the heat transfer resistance in the heat transfer path from the insulating substrate 1 to the heat sink 8 also increases, so that depending on the thermal conductivity of the insulating layer 7, There is a restriction in increasing the thickness d of the layer 7 to enhance the insulating property of the end face of the side surface.
(D) The present invention has been made to solve the above-described problems, in an insulating substrate having an insulating layer formed by spraying ceramic powder on one surface of a conductive base material. An object of the present invention is to improve the insulating property of the side surface end face with a simple structure and low cost, and to provide a method for manufacturing the insulating substrate, a semiconductor module and a semiconductor device using the insulating substrate.

  In order to solve the above-mentioned problems, the present inventor used a ceramic sprayed film having good adhesion as an insulating layer by causing ceramic powder as a spraying raw material to collide with a substrate at a high temperature and high speed by, for example, plasma spraying. With respect to the insulating substrate (conductive substrate with an insulating layer) formed on one surface of the conductive base material, the insulating structure of the end face of the side surface portion was studied, and the present invention was completed.

  In order to achieve the above object, according to the present invention, there is provided an insulating substrate including an insulating layer formed by spraying ceramic powder on a first surface of a conductive base material having a first surface and a second surface. A semiconductor device in which at least one semiconductor circuit element is mounted in direct or indirect contact with the second surface of the conductive substrate and a metal member is attached in close contact with the surface of the insulating layer. In the insulating substrate used for constituting the conductive substrate, the conductive base material has a notch at a corner on the first surface side, and the ceramic powder is sprayed also on the notch. And a bottom surface parallel to the first surface is formed on the second surface side of the notch, and faces the bottom surface. The ceramic powder is sprayed from the direction to An insulating substrate is characterized in that an edge layer is formed.

  According to the above invention, the “insulation creepage distance between the conductive base material and the metal member” in a state in which the metal member is attached in close contact with the surface of the insulating layer is larger than the “thickness of the insulating layer”. It has a structure. In a semiconductor device, there is a limit to increasing the thickness of the insulating layer in order to reduce the heat transfer resistance in the heat transfer path from the insulating substrate to a metal member such as a heat sink, but in the present invention to which the above structure is applied, there is a limit to the insulating layer. The insulation creepage distance can be increased without being limited by the thickness, and the insulation of the side surface end face of the insulating substrate can be improved. A metal member such as a heat sink is attached to a semiconductor module using the insulating substrate. The insulating property of the semiconductor device to be configured can be further improved. By using such an insulating substrate, it is possible to realize a semiconductor module and a semiconductor device that can maintain good insulation and can reduce the cost of members.

  Further, in the above-mentioned insulating substrate, aluminum oxide powder is used as the ceramic powder, and the insulating layer is formed by spraying the aluminum oxide powder, and the thermal conductivity is increased by heat treatment. It can also be an insulating substrate characterized by being an insulating layer.

  In the above invention, since the insulation of the side surface end face can be improved while keeping the thickness of the insulating layer in the insulating substrate small, in the semiconductor device, in the heat transfer path from the insulating substrate to a metal member such as a heat sink, for example. Heat transfer resistance can be kept low. Further, since the insulating layer has a higher thermal conductivity, the heat transfer resistance can be suppressed to a lower level, and a semiconductor device with better heat dissipation can be realized. become able to.

  Furthermore, in the above insulating substrate, aluminum oxide powder is used as the ceramic powder, and the insulating layer is formed by spraying the aluminum oxide powder and has a hexagonal crystal structure. It can also be an insulating substrate characterized by being an insulating layer.

  In the above invention, since the insulation of the side surface end face can be improved while keeping the thickness of the insulating layer in the insulating substrate small, in the semiconductor device, in the heat transfer path from the insulating substrate to a metal member such as a heat sink, for example. Heat transfer resistance can be kept low. Further, since the insulating layer has a higher thermal conductivity, the heat transfer resistance can be suppressed to a lower level, and a semiconductor device with better heat dissipation can be realized. become able to.

  Furthermore, in the above insulating substrate, the insulating layer may have a thickness of 80 μm to 300 μm.

  Furthermore, as a configuration of a semiconductor module using the above insulating substrate, at least one or more semiconductors mounted in direct or indirect contact with the insulating substrate and the second surface of the conductive base material A circuit element can be provided.

Furthermore, in the above semiconductor module, a surface other than the first surface of the conductive base material is sealed with a sealing agent that is an insulating material together with the semiconductor circuit element mounted on the second surface. And it can be set as the structure which has the insulating surface which covers the said electroconductive base material with the said sealing agent and the said insulating layer formed on the said 1st surface.
Furthermore, as a configuration of the semiconductor device using the above-described semiconductor module, a cooling metal member may be closely attached to the exposed surface of the insulating layer in the semiconductor module.

  In addition, in order to achieve the above object, according to the present invention, a notch processing step of forming a notch at a corner on the first surface side of the conductive substrate having the first surface and the second surface, After the notch processing step, an insulating layer forming step of forming an insulating layer on the first surface of the conductive base material and on the notch portion by spraying ceramic powder, and after the insulating layer forming step A grinding step of grinding the insulating layer formed on the first surface to align the surfaces of the insulating layer on the first surface and the insulating layer of the notch, and after the grinding step Mounting at least one semiconductor circuit element in direct or indirect contact with the second surface of the conductive base material and applying a metal member to the surface of the insulating layer formed on the first surface With semiconductor module manufacturing process In the notch processing step, a bottom surface parallel to the first surface is formed on the second surface side of the notch, and in the insulating layer forming step, the ceramic powder is sprayed from a direction facing the bottom surface. And forming the insulating layer.

  Further, in the above method for manufacturing an insulating substrate, an aluminum oxide powder is used as the ceramic powder, and after the insulating layer forming step, the insulating layer is heat-treated by heat treatment. It can be set as the structure provided with the process of raising a rate.

  Further, in the above method for manufacturing an insulating substrate, an aluminum oxide powder is used as the ceramic powder, and the method further comprises a step of making the crystal structure of the insulating layer hexagonal after the insulating layer forming step. It can be configured.

  According to the present invention, the insulation creepage distance can be increased without being restricted by the thickness of the insulating layer at the side surface end face of the insulating substrate provided with the insulating layer formed by spraying ceramic powder on one surface of the conductive substrate. The insulating property can be improved by increasing the size, and by using this insulating substrate, it is possible to realize a semiconductor module and a semiconductor device capable of maintaining good insulating properties and reducing the cost of members.

It is a figure which shows the structural example of the insulated substrate, semiconductor module, and semiconductor device by the 1st reference form of this invention. It is a figure which shows the structural example of the manufacturing method of the insulated substrate by the 1st reference form of this invention, a semiconductor module, and a semiconductor device. It is a figure which shows the evaluation test method of the dielectric breakdown characteristic of the insulated substrate by the 1st reference form of this invention. It is a figure which shows the structural example of the insulated substrate by the 2nd reference form of this invention, a semiconductor module, and a semiconductor device. It is a figure which shows the structural example of the manufacturing method of the insulated substrate by the 2nd reference form of this invention, a semiconductor module, and a semiconductor device. It is a figure which shows the structural example of the insulated substrate, semiconductor module, and semiconductor device by embodiment of this invention. It is a figure which shows the structural example of the manufacturing method of the insulated substrate, semiconductor module, and semiconductor device by embodiment of this invention. It is a figure which shows the example of a different structure of the manufacturing method of the insulated substrate by embodiment of this invention. It is a figure which shows the structural example of the semiconductor module by a prior art. It is a figure which shows the example of a different structure of the semiconductor module by a prior art.

Next, an embodiment of the present invention will be described with reference to FIGS. In addition, this invention is not limited to the following embodiment, In the range which does not change the summary, it can implement suitably. In the following description, common parts or elements are denoted by common reference symbols throughout the drawings unless otherwise specified. In the drawings, each element of each embodiment is not necessarily shown in a scale ratio.
Embodiment of the present invention
<First Reference Form>
Hereinafter, a first reference embodiment of the present invention will be described with reference to the drawings.

(A) Configuration example of insulating substrate, semiconductor module, and semiconductor device:
FIG. 1 is a cross-sectional view showing a configuration of an insulating substrate 11A, a semiconductor module 21A, and a semiconductor device 31A according to the first embodiment, and FIG. 1 (a) is a cross-sectional view showing the overall configuration, and FIG. ) Is an enlarged cross-sectional view of a portion C1 in FIG.

  As shown in FIG. 1, an insulating layer 7Aa is formed on the first surface 1a (lower surface in the drawing) of the conductive substrate 1A. On the other hand, the semiconductor circuit elements 2 and 2 are mounted on the second surface 1b (the upper surface in the drawing) of the conductive substrate 1A so as to be in direct or indirect contact therewith.

  More specifically, in the first reference embodiment, the conductive substrate 1A is made of a copper plate. The shape of the conductive substrate 1A is, for example, a flat plate having a thickness of approximately 1 mm to 5 mm, and is square or rectangular in plan view. The insulating layer 7Aa is a layer or film formed by depositing aluminum oxide (alumina) powder 71 by a thermal spraying method (hereinafter, also simply referred to as “layer”). And insulating layer 7Aa is formed so that it may have a thickness of 80-300 micrometers by spraying the powder 71 of aluminum oxide on the 1st surface 1a of 1 A of electroconductive base materials. The thickness of the insulating layer is preferably 80 to 300 μm, and if the thickness is within this range, the insulating layer itself (bulk) has sufficient withstand voltage characteristics and the insulating layer has sufficient heat transfer resistance. Can be lowered.

  The conductive substrate 1A has a tapered surface 1Ac at the corner on the first surface 1a side, and an insulating layer 7Ab formed by thermal spraying of the ceramic powder 71 is also formed on the tapered surface 1Ac. And is formed so as to be continuous. Then, an insulating substrate 11A is configured as a conductive base material with an insulating layer including an insulating layer 7A including an insulating layer 7Aa and an insulating layer 7Ab on the first surface 1a side of the conductive base material 1A. Here, as shown in FIG. 1B, the inclination angle of the taper surface 1Ac, that is, the angle between the taper surface 1Ac and the direction perpendicular to the bottom surface of the conductive substrate 1A is defined as θ.

  As will be described later, it is preferable to increase the thermal conductivity of the insulating layer by performing “heat treatment” after the insulating layer 7A is formed. When the crystal structure of the insulating layer after this “heat treatment” is analyzed by an X-ray diffractometer, a hexagonal diffraction peak of aluminum oxide can be confirmed.

  The semiconductor circuit elements 2 and 2 which are power semiconductor elements, such as IGBT, are joined to the 2nd surface 1b of 1 A of conductive base materials, for example with solder, and the 2nd surface of the conductive base material 1 is directly or indirectly. It is mounted so as to contact the surface 1b. The connection terminals (not shown) of the semiconductor circuit elements 2 and 2 are electrically connected to the lead frame 6 by a bonding wire 4 made of an aluminum wire having a wire diameter of 125 to 500 μm, for example. Then, each of the above-described elements, that is, the insulating substrate 11A, the semiconductor circuit elements 2 and 2, the lead frame 6, and the bonding wire 4 are made of, for example, an epoxy resin in which an inorganic filler is mixed, and a molding resin 5 for sealing. The semiconductor module 21A is configured.

  The semiconductor module 21A configured as described above is sealed by covering all surfaces other than the first surface 1a of the conductive substrate 1A together with the semiconductor circuit elements 2 and 2 with the molding resin 5 which is an insulating material. ing. Therefore, on the surface of the semiconductor module 21A, only the insulating layer 7Aa formed on the molding resin 5 and the first surface 1a is in contact with the outside world except for the end 62 of the lead frame 6 for electrical connection. That is, the surface of the semiconductor module 21A is an insulating surface that insulates the conductive substrate 1A from the outside.

  The semiconductor module 21A is attached to the heat sink 8 so that the exposed surface of the insulating layer 7Aa is in close contact with each other, thereby forming a semiconductor device 31A.

(B) Insulating property of side surface end face in insulating substrate:
In the insulating structure of the side surface end face in the insulating substrate 11A shown in FIG. 1B, for example, “the thickness dA2 in the direction perpendicular to the insulating substrate 11A in the insulating layer 7Ab on the tapered surface 1Ac” is “on the first surface 1a”. Is equal to the “thickness d of the insulating layer 7Aa”, the “insulating creepage distance dA = dA1 + dA2 between the conductive substrate 1A and the heat sink 8” is equal to “the creepage length dA1 of the insulating layer 7Ab on the tapered surface 1Ac”. The creepage distance is greater than the thickness d ”of the insulating layer 7Aa on the first surface 1a.

  As described above, in the first reference embodiment, the insulating creepage distance between the conductive base material 1A and the heat sink 8 is made larger than the thickness of the insulating layer 7Aa to improve the insulating property of the side surface end face of the insulating substrate 11A. Can do. A semiconductor device 31A configured by attaching a metal member 8 such as a heat sink to the semiconductor module 21A using such an insulating substrate 11A has better insulation.

  Further, the insulating property of the side surface end face of the insulating substrate 11A depends not only on the above-mentioned insulating creepage distance but also on the inclination angle (taper angle) θ of the tapered surface 1Ac. In the present invention, the inclination angle θ of the tapered surface 1Ac is preferably 30 ° to 80 °, and more preferably 50 ° to 70 °. When the inclination angle θ is 50 ° to 70 °, sufficiently stable dielectric breakdown characteristics without dielectric breakdown at the end face of the insulating substrate 11A can be obtained, and a resin in a semiconductor module using the insulating substrate 11A can be obtained. Sealability can also be made sufficiently good.

(C) Configuration example of manufacturing method of insulating substrate, semiconductor module, and semiconductor device:
FIG. 2 is a cross-sectional view illustrating a configuration example of a method of manufacturing the insulating substrate 11A, the semiconductor module 21A, and the semiconductor device 31A according to the first reference order in the order of steps. In FIG. 2D and FIG. 2E, the bonding wire 4 and the lead frame 6 are omitted from the components of the semiconductor module 21A.

  (C1) First, a flat plate-like conductive member such as a copper plate having a thickness of approximately 1 mm to 5 mm is punched out by, for example, pressing, and formed into a necessary shape as a conductive base material, and further formed into a necessary shape. As shown in FIG. 2A, the entire periphery of the corner of the conductive base material on the first surface 1a side is tapered as shown in FIG. 2A to form a conductive base material 1A having a tapered surface 1Ac. To do.

  (C2) Next, as an insulating layer forming step, an insulating layer 7A is formed on the first surface 1a and the tapered surface 1Ac of the conductive substrate 1A. As shown in FIG. 2B, the insulating layer 7A is formed by depositing aluminum oxide (alumina) powder 71 using a thermal spraying method. Specifically, the raw material powder 71 is sprayed from one direction toward the conductive substrate 1 </ b> A while preventing adhesion to unnecessary portions by the mask M in the atmosphere or an atmosphere under reduced pressure. As the raw material powder 71 in this case, α-alumina powder, that is, corundum (for example, 99.7% purity alumina powder) is typically used. In this way, as shown in FIG. 2C, the insulating substrate 1A in which the insulating layer 7Aa is formed on the first surface 1a of the conductive base material 1A and the insulating layer 7Ab is formed on the tapered surface 1Ac. Is produced. As a thermal spraying method used for this treatment, it is desirable to employ a plasma spraying method suitable for thermal spraying of an insulating material, but other thermal spraying methods can also be used. The thickness of the insulating layer 7A can be appropriately adjusted according to the supply rate of the raw material powder and the spraying time among the conditions of the spraying process.

  (C3) Next, as a manufacturing process of the semiconductor module 21A using the insulating substrate 11A, as shown in FIG. 2D, the surface of the insulating layer 7Aa in the insulating substrate 11A using the molding resin 5 for sealing. The semiconductor module 21A is formed by resin-sealing the second surface 1b and the side surface of the conductive base material 1A so as to be exposed.

  More specifically, the manufacturing process of the semiconductor module 21A can be performed, for example, as follows (see FIG. 1A).

  First, the semiconductor circuit elements 2 and 2 are mounted on the second surface 1b of the conductive substrate 1A. Here, the semiconductor circuit elements 2 and 2 are joined to the second surface 1b of the conductive substrate 1A by soldering. This soldering is performed in a furnace capable of hydrogen reduction using pellet-shaped solder. The reason for using a furnace capable of hydrogen reduction is to improve the wettability with the solder by removing the oxide film on the second surface 1b of the conductive substrate 1A by hydrogen reduction and activating the surface. . As the solder material, for example, high-temperature solder made of SnPbAg, lead-free solder made of SnAgCu or SnCuNi is used. The soldering temperature is appropriately set according to the melting point of the solder used in the joining process. Further, if voids (bubbles) remain in the solder layer of this joint, the thermal resistance increases. Therefore, in this embodiment, the pressure is reduced so that the ultimate vacuum is 10 Torr, that is, about 1330 Pa or less in a state where the solder is melted so that voids are not generated, and the temperature is lowered as it is to solidify the solder. Complete.

  Next, the semiconductor circuit elements 2 and 2 and the lead frame 6 are connected by the bonding wire 4. The connection process using the bonding wire 4 is performed by connecting the lead frame 6 and the connection pads (not shown) of the semiconductor circuit elements 2 and 2 by a known ultrasonic bonding method.

  Finally, sealing with resin is performed by a transfer molding method. In this sealing process, first, circuit components are arranged inside a mold (not shown). At this time, the temperature of the mold is set to about 170 to 180 ° C. in advance. Next, the molding resin preheated to an appropriate temperature is poured into the mold by a plunger. Any known resin material can be used as the material of the molding resin. In this embodiment, an epoxy resin in which an inorganic filler is mixed is employed. The molding resin material has a tablet-like appearance before molding. As the inorganic filler, particles or powders of one or more materials of the group consisting of silicon oxide, aluminum oxide, silicon nitride, aluminum nitride, and boron nitride are applicable. As the material of the molding resin, a material having higher thermal conductivity is more desirable as long as other required performance is satisfied. As an example, a material having a thermal conductivity of 0.5 to 5 W / m · K is a suitable material. Curing of the molding resin starts several tens of seconds after the molding resin is poured. Immediately after this, the circuit component sealed with the molding resin is removed from the mold, and then a post-curing process is performed. This post-curing treatment is performed by heating a circuit component sealed with a molding resin in a thermostatic bath. As described above, the sealing process is completed, and the manufacturing process of the semiconductor module 21A is completed.

  (C4) Next, as a manufacturing process of the semiconductor device 31A, as shown in FIG. 2E, the semiconductor module 21A is placed on the heat sink (metal member) 8, and the exposed surface of the insulating layer 7Aa is the heat sink (metal member) 8. The semiconductor device 31A is formed by attaching so as to be in close contact with each other.

Reference example 1

  In the insulating substrate, the semiconductor module, and the semiconductor device according to the first embodiment of the present invention, the difference in the inclination angle of the end face of the insulating layer, that is, the inclination angle (taper angle) θ of the taper surface 1Ac of the conductive substrate 1A is the insulation characteristic. In order to investigate the influence, samples of insulating structures with different inclination angles of the insulating layer end faces were prepared as follows, and the respective dielectric breakdown characteristics were evaluated.

  First, a sample having an insulating structure was prepared as follows. That is, an insulating layer 7A is formed by spraying aluminum oxide (alumina) powder 71 on the first surface 1a side (see FIG. 2) of the conductive base material 1A made of a copper material (copper plate) to form an insulating substrate 11A ( (Alumina sprayed insulating layer copper block) is formed, and the creeping surface of the side surface portion of the insulating substrate 11A is sealed with an epoxy-based sealing agent (molding resin) 5, and then the member is cured, as shown in FIG. An insulation structure sample was prepared. Here, the film thickness of the insulating layer 7A by the thermal spraying of alumina was 0.12 mm. In addition, regarding the inclination angle θ (see FIG. 1B) of the taper surface 1Ac of the conductive substrate 1A, three samples each having 45 °, 60 °, and 75 ° were prepared, and samples A1 to A3 were respectively prepared. , B1 to B3, and C1 to C3 (see Table 1).

  In addition, as electroconductive base material 1A which comprises samples A1 to A3 (θ = 45 °), B1 to B3 (θ = 60 °), and C1 to C3 (θ = 75 °), all have a large overall shape. In which the thickness dimension L1, the width dimension L2 and the depth dimension not shown in FIG. 2A are the same. Then, in the samples A1 to A3, B1 to B3, and C1 to C3, the conductive substrate 1A in FIG. 2A is used so that the contact area of the insulating substrate 11A with the heat sink (metal member) 8 is the same for each sample. The taper machining was performed under the condition that the width L2a of the remaining portion after taper machining on the first surface 1a and the depth dimension (not shown) were the same.

Also, as the sealant 5, and a thermal deformation temperature of 175 ° C. or higher, the thermal expansion coefficient is that ^{1.5 × 10 -5 /℃~1.8×10 -5 / ℃} , bond strength An epoxy resin of 10-30 MPa was used.

  The samples A1 to A3, B1 to B3, and C1 to C3 prepared as described above were subjected to a dielectric breakdown test using a dielectric breakdown test apparatus. In the dielectric breakdown test, as shown in FIG. 3, for each sample, electrodes 201A and 201B made of a copper adhesive tape were applied to the copper substrate surface of the conductive base material 1A and the surface of the insulating layer 7A, respectively, and the dielectric breakdown test was performed. The dielectric breakdown voltage (BDV) was measured as dielectric breakdown characteristics, and the dielectric breakdown location was visually confirmed. In FIG. 3, reference numerals 202A and 202B denote electrodes of a dielectric breakdown test apparatus.

  Table 1 shows the results of evaluating the dielectric breakdown characteristics of each of the above samples. As shown in Table 1, when the inclination angle θ of the end face is 60 ° or more, there is no dielectric breakdown at the end face, and more stable dielectric breakdown characteristics than when the inclination angle θ of the end face is 45 °. Obtained. From this evaluation result, the inclination angle of the side surface end surface of the insulating substrate 11A (copper block with an alumina sprayed insulating layer), that is, the taper surface 1Ac of the conductive substrate 1A (copper block) and the bottom surface of the conductive substrate 1A. It was confirmed that particularly good dielectric breakdown characteristics were obtained when the angle θ formed with the vertical direction was 60 ° to 75 °.

  In addition, regarding the above-described evaluation result regarding the dielectric breakdown characteristics, the side surface end surface (inclination with respect to the surface of the heat sink (metal member) 8 in FIG. 2E) becomes smaller as the inclination angle θ of the side surface end surface of the insulating substrate 11A becomes smaller. As the surface becomes closer to the vertical), electric field concentration at the corners of the insulating substrate 11A in contact with the surface of the heat sink 8 (that is, the portion in the round frame P1 in FIG. It is considered that the (inclined surface) insulation is lower.

  In addition, as the film quality of the insulating layer 7Ab formed on the tapered surface 1Ac of the conductive base material 1A by thermal spraying of alumina in the samples A1 to A3, B1 to B3, and C1 to C3, the inclination angle θ of the tapered surface 1Ac is 45 °. The deterioration of the film quality is confirmed in samples A1 to A3.

  On the other hand, as the inclination angle θ of the end surface of the side surface of the insulating substrate 11A increases (that is, as the end surface (inclined surface) of the side surface portion becomes parallel to the surface of the heat sink 8 in FIG. 2E), the insulating substrate 11A is used. The resin sealing property by the molding resin 5 in the existing semiconductor module is lowered.

Therefore, a sufficiently stable dielectric breakdown characteristic with no dielectric breakdown at the end face of the insulating substrate can be obtained, and an angle of inclination such that the resin sealing property in a semiconductor module using the insulating substrate is sufficiently good. As the range of θ, 50 ° to 70 ° is considered particularly suitable.
<Second Reference Form>
Hereinafter, a second reference embodiment of the present invention will be described with reference to the drawings.

(A) Configuration example of insulating substrate, semiconductor module, and semiconductor device:
FIG. 4 is a cross-sectional view showing the configuration of the insulating substrate 11B, the semiconductor module 21B, and the semiconductor device 31B according to the second embodiment, and FIG. 4A is a cross-sectional view showing the overall configuration, and FIG. ) Is an enlarged cross-sectional view of a portion C2 in FIG.

  As shown in FIG. 4, an insulating layer 7B is formed on the first surface 1a (the lower surface in the figure) of the conductive substrate 1B. On the other hand, the semiconductor circuit elements 2 and 2 are mounted on the second surface 1b (the upper surface in the drawing) of the conductive substrate 1B so as to be in direct or indirect contact.

  More specifically, in the second reference embodiment, the conductive substrate 1B is made of a copper plate. The shape of the conductive substrate 1B is, for example, a flat plate having a thickness of approximately 1 mm to 5 mm, and is square or rectangular in plan view. The insulating layer 7B is a layer or film formed by depositing aluminum oxide (alumina) powder 71 by a thermal spraying method (hereinafter, also simply referred to as “layer”). The insulating layer 7B is formed to have a thickness of 80 to 300 μm by spraying an aluminum oxide powder 71 on the first surface 1a of the conductive substrate 1B. The thickness of the insulating layer is preferably 80 to 300 μm, and if the thickness is within this range, the insulating layer itself (bulk) has sufficient withstand voltage characteristics and the insulating layer has sufficient heat transfer resistance. Can be lowered.

  The conductive substrate 1B has a notch 1Bc at a corner on the first surface 1a side, and the insulating layer 7B on the first surface 1a extends outward from a portion in contact with the conductive substrate 1B. It is comprised so that it may become. And the insulating substrate 11B is comprised as an electroconductive base material with an insulating layer provided with the insulating layer 7B in the 1st surface 1a side of the electroconductive base material 1B.

  As will be described later, it is preferable to increase the thermal conductivity of the insulating layer by performing “heat treatment” after the insulating layer 7B is formed. When the crystal structure of the insulating layer after this “heat treatment” is analyzed by an X-ray diffractometer, a hexagonal diffraction peak of aluminum oxide can be confirmed.

  The configuration of the semiconductor module 21B in which the insulating substrate 11B, the semiconductor circuit elements 2 and 2, the lead frame 6, and the bonding wire 4 are sealed with the molding resin 5 has been described for the semiconductor module 21A in the first reference embodiment. The configuration is the same.

  Then, the semiconductor module 21B is attached to the heat sink 8 so that the exposed surface of the insulating layer 7B is in close contact with each other, thereby forming a semiconductor device 31B.

(B) Insulating property of side surface end face in insulating substrate:
In the insulating structure of the end surface of the side surface portion of the insulating substrate 11B shown in FIG. 4B, “the thickness dB2 of the portion extending outward from the portion of the insulating layer 7B in contact with the conductive substrate 1B” is “first”. When it is equal to “thickness d of insulating layer 7B on one surface 1a”, “insulating creepage distance dB = dB1 + dB2 between conductive substrate 1B and heat sink 8” is larger than “a portion in contact with conductive substrate 1B”. The creepage distance is larger than the “thickness d of the insulating layer 7B on the first surface 1a” by the extension length dB1 of the insulating layer 7B extending outward.

  As described above, in the second reference embodiment, as in the first reference embodiment described above, the insulating creepage distance between the conductive base material 1B and the heat sink 8 is made larger than the thickness of the insulating layer 7B. The insulation of the side surface end face in 11B can be improved. And the semiconductor device 31B comprised by attaching the metal members 8, such as a heat sink, to the semiconductor module 21B using such an insulating substrate 11B has more excellent insulation.

(C) Configuration example of manufacturing method of insulating substrate, semiconductor module, and semiconductor device:
FIG. 5 is a cross-sectional view illustrating a configuration example of a method of manufacturing the insulating substrate 11B, the semiconductor module 21B, and the semiconductor device 31B according to the second reference embodiment in the order of steps. In FIG. 5D and FIG. 5E, the bonding wire 4 and the lead frame 6 are omitted from the components of the semiconductor module 21B.

  (C1) First, a plate-like conductive member such as a copper plate having a thickness of approximately 1 mm to 5 mm is punched out by, for example, pressing, and formed into a necessary shape as a conductive substrate to obtain the conductive substrate 1. .

  (C2) Next, as an insulating layer forming step, an insulating layer 7B is formed on the first surface 1a of the conductive substrate 1. As shown in FIG. 5A, the insulating layer 7B is formed by depositing aluminum oxide (alumina) powder 71 using a thermal spraying method. Specifically, the raw material powder 71 is sprayed from one direction toward the conductive substrate 1 </ b> A while preventing adhesion to unnecessary portions by the mask M in the atmosphere or an atmosphere under reduced pressure. As the raw material powder 71 in this case, α-alumina powder, that is, corundum (for example, 99.7% purity alumina powder) is typically used. Thus, the insulating layer 7B is formed on the first surface 1a of the conductive substrate 1 as shown in FIG. As a thermal spraying method used for this treatment, it is desirable to employ a plasma spraying method suitable for thermal spraying of an insulating material, but other thermal spraying methods can also be used. The thickness of the insulating layer 7B can be appropriately adjusted according to the supply rate of the raw material powder and the thermal spraying time among the thermal spraying treatment conditions.

  (C3) Next, as a notch processing step, as shown in FIG. 5C, a concave notch 1 </ b> Bc is formed on the entire periphery of the corner on the first surface 1 a side of the conductive substrate 1. The machining for forming the notch 1Bc may be either mechanical cutting or etching.

  By this notch processing, the conductive substrate 1 becomes a conductive substrate 1B having a notch 1Bc at the corner on the first surface 1a side. Then, the insulating substrate 11B is provided as an electrically conductive substrate with an insulating layer provided with an insulating layer 7B extending outward from a portion in contact with the electrically conductive substrate 1B on the first surface 1a side of the electrically conductive substrate 1B. Composed.

  (C4) Next, as a manufacturing process of the semiconductor module 21B using the insulating substrate 11B, as shown in FIG. 5D, the surface of the insulating layer 7B on the insulating substrate 11B using the molding resin 5 for sealing. As a result, the second surface 1b and the side surface of the conductive substrate 1B are resin-sealed to form the semiconductor module 2B.

  A more specific configuration of the manufacturing process of the semiconductor module 21B is the same as the specific configuration described for the manufacturing process of the semiconductor module 21A in the first reference embodiment.

(C5) Next, as a manufacturing process of the semiconductor device 31B, as shown in FIG. 5E, the semiconductor module 21B is placed on the heat sink (metal member) 8, and the exposed surface of the insulating layer 7B is the heat sink (metal member) 8. The semiconductor device 31B is formed by attaching so as to be in close contact with the semiconductor device 31B.
<Embodiment according to the present invention>
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(A) Configuration example of insulating substrate, semiconductor module, and semiconductor device:
FIG. 6 is a cross-sectional view showing the configuration of the insulating substrate 11C, the semiconductor module 21C, and the semiconductor device 31C according to the embodiment of the present invention, and FIG. 6A is a cross-sectional view showing the overall configuration, and FIG. ) Is an enlarged cross-sectional view of a portion C3 in FIG.

  As shown in FIG. 6, an insulating layer 7Ca is formed on the first surface 1a (the lower surface in the drawing) of the conductive substrate 1C. On the other hand, the semiconductor circuit elements 2 and 2 are mounted on the second surface 1b (the upper surface in the drawing) of the conductive substrate 1C so as to be in direct or indirect contact therewith.

  More specifically, in the embodiment of the present invention, the conductive substrate 1C is made of a copper plate. The shape of the conductive substrate 1C is, for example, a flat plate having a thickness of approximately 1 mm to 5 mm, and is square or rectangular in plan view. The insulating layer 7Ca is a layer or film formed by depositing aluminum oxide (alumina) powder 71 by a thermal spraying method (hereinafter, also simply referred to as “layer”). The insulating layer 7Ca is formed to have a thickness of 80 to 300 [mu] m by spraying aluminum oxide powder 71 on the first surface 1a of the conductive substrate 1C. The thickness of the insulating layer is preferably 80 to 300 μm, and if the thickness is within this range, the insulating layer itself (bulk) has sufficient withstand voltage characteristics and the insulating layer has sufficient heat transfer resistance. Can be lowered.

  The conductive substrate 1C has a notch 1Cc at a corner on the first surface 1a side, and an insulating layer 7Cb formed by thermal spraying of the ceramic powder 71 is also insulated on the first surface 1a on the notch 1Cc. It is formed so as to be continuous with the layer 7Ca. Then, an insulating substrate 11C is configured as a conductive base material with an insulating layer including an insulating layer 7C composed of an insulating layer 7Ca and an insulating layer 7Cb on the first surface 1a side of the conductive base material 1C. Here, it is preferable that the bottom surface of the cutout portion 1Cc in the conductive substrate 1C is formed as a surface parallel to the first surface 1a.

  As will be described later, it is preferable to increase the thermal conductivity of the insulating layer by performing “heat treatment” after the insulating layer 7C is formed. When the crystal structure of the insulating layer after this “heat treatment” is analyzed by an X-ray diffractometer, a hexagonal diffraction peak of aluminum oxide can be confirmed.

  The configuration of the semiconductor module 21C in which the insulating substrate 11C, the semiconductor circuit elements 2 and 2, the lead frame 6, and the bonding wire 4 are sealed with the molding resin 5 has been described for the semiconductor module 21A in the first reference embodiment. The configuration is the same.

  The semiconductor module 21C is attached to the heat sink 8 so that the exposed surface of the insulating layer 7C is in close contact with each other, thereby forming a semiconductor device 31C.

(B) Insulating property of side surface end face in insulating substrate:
In the insulating structure of the side surface portion end surface of the insulating substrate 11C shown in FIG. 6B, “the insulating creepage distance dC = dC1 + dC2 between the conductive base material 1C and the heat sink 8” is “the first surface in the notch portion 1Cc”. The creepage distance is larger than the “thickness d (= dC2) of the insulating layer 7Ca” by the notch depth length dC1 ”from 1a.

  As described above, in the embodiment of the present invention, the insulating creepage distance between the conductive base material 1C and the heat sink 8 is made larger than the thickness of the insulating layer 7Ca in the same manner as in the first reference embodiment described above. It is possible to improve the insulating property of the side surface end face in 11C. A semiconductor device 31C configured by attaching a metal member 8 such as a heat sink to the semiconductor module 21C using such an insulating substrate 11C has more excellent insulating properties.

(C) Configuration example of manufacturing method of insulating substrate, semiconductor module, and semiconductor device:
FIG. 7 is a cross-sectional view illustrating a configuration example of a method of manufacturing the insulating substrate 11C, the semiconductor module 21C, and the semiconductor device 31C according to the embodiment of the present invention in the order of steps. 7E and 7F, illustration of the bonding wire 4 and the lead frame 6 among the components of the semiconductor module 21C is omitted.

  (C1) First, a flat plate-like conductive member such as a copper plate having a thickness of approximately 1 mm to 5 mm is punched out by, for example, pressing, and formed into a necessary shape as a conductive base material, and further formed into a necessary shape. Cutout portions 1Cc are formed in the entire periphery of the corner portion on the first surface 1a side of the conductive substrate thus obtained, to obtain the conductive substrate 1C. The machining for forming the notch 1Cc may be either mechanical cutting or etching.

  (C2) Next, as an insulating layer forming step, an insulating layer (sprayed layer) 7C1 is formed on the first surface 1a and the cutout portion 1Cc of the conductive substrate 1C. As shown in FIG. 7B, the insulating layer (sprayed layer 7C1) is formed by depositing aluminum oxide (alumina) powder 71 using a spraying method. Specifically, the raw material powder 71 is sprayed from one direction toward the conductive substrate 1 </ b> C while preventing adhesion to unnecessary portions by the mask M in the atmosphere or an atmosphere under reduced pressure. As the raw material powder 71 in this case, α-alumina powder, that is, corundum (for example, 99.7% purity alumina powder) is typically used. In this way, as shown in FIG. 7C, the insulating layer (sprayed layer) 7C1a is formed on the first surface 1a of the conductive substrate 1C, and the insulating layer (sprayed layer) is formed on the notch 1Cc. ) 7C1b is formed. As a thermal spraying method used for this treatment, it is desirable to employ a plasma spraying method suitable for thermal spraying of an insulating material, but other thermal spraying methods can also be used. The thickness of the insulating layer (sprayed layer) 7C1 can be appropriately adjusted according to the supply rate of the raw material powder and the spraying time, among the conditions of the spraying process.

  (C3) Next, as a grinding process, the insulating layer (sprayed layer) 7C1a formed on the first surface 1a is ground to the level indicated by the D1-D1 line in FIG. The surfaces of the upper insulating layer 7Ca and the insulating layer 7Cb on the notch 1Cc are aligned. In this way, as shown in FIG. 7D, the insulating substrate 11C having the insulating layer 7C composed of the insulating layer 7Ca and the insulating layer 7Cb on the first surface 1a side of the conductive base material 1C is manufactured. .

  (C4) Next, as a manufacturing process of the semiconductor module 21C using the insulating substrate 11C, as shown in FIG. 7E, the surface of the insulating layer 7C in the insulating substrate 11C using the molding resin 5 for sealing. The semiconductor module 21C is formed by resin-sealing the second surface 1b and the side surface of the conductive base material 1C so that is exposed.

  A more specific configuration of the manufacturing process of the semiconductor module 21C is the same as the specific configuration described for the manufacturing process of the semiconductor module 21A in the first reference embodiment.

  (C5) Next, as a manufacturing process of the semiconductor device 31C, as shown in FIG. 7F, the semiconductor module 2C is placed on the heat sink (metal member) 8, and the exposed surface of the insulating layer 7C is the heat sink (metal member) 8. The semiconductor device 31C is formed by being attached so as to be in close contact with each other.

(D) Configuration examples of different methods for manufacturing an insulating substrate:
FIG. 8 is a cross-sectional view illustrating different configuration examples of the method of manufacturing the insulating substrate 1C according to the embodiment of the present invention in the order of steps.

  (D1) First, as a notch groove forming step for the first surface 101a of the conductive plate-like member 101C made of a copper plate having a thickness of approximately 1 mm to 5 mm and having the first surface 101a and the second surface 101b, FIG. As shown in FIG. 8 (a), the conductive plate-like member 101C is separated into a plurality of conductive substrates (not shown in FIG. 8 (a)). A notch groove 101Cc is formed.

  (D2) Next, as shown in FIG. 8 (b), as shown in FIG. 8 (b), for example, by spraying ceramic powder 71 by a plasma spraying method, as shown in FIG. An insulating layer (sprayed layer) 107C1 is formed on the first surface 101a of 101C and the notch groove 101Cc. The specific configuration of the thermal spraying method in this insulating layer forming step is the same as the specific configuration described with reference to FIG. 7B. However, the thermal spraying process is not performed on the individual conductive substrate 1C, but a plurality of conductive substrates. The difference is that the thermal spraying process is performed on the conductive plate-like member 101C before being separated into 1C.

  (D3) Next, as a grinding step, the insulating layer (sprayed layer) 107C1 is ground to the level indicated by the line D2-D2 in FIG. 8C, so that the insulating layer 107Ca and the notch groove 107Cc on the first surface 101a are ground. The conductive plate member 111C with an insulating layer is formed by aligning the surface with the upper insulating layer 107Cb.

  (D4) Next, as the separation step, as shown by the white arrow line S in FIG. 8D, the conductive plate member 111C with an insulating layer is cut along the separation line, and FIG. Are separated into a plurality of insulating substrates 11C.

The above-described manufacturing method shown in FIG. 8 can perform thermal spraying on a plurality of conductive substrates in a single process. Therefore, when considering labor saving in the insulating layer forming step, the insulating plate 11C can be manufactured at a lower cost. It is suitable for enabling manufacture.
[Contrast of Configuration of Embodiment of Present Invention and Other Configuration Examples]
(A) The specific configuration of the insulating substrate (conductive substrate with an insulating layer) according to the present invention is shown in the first and second reference embodiments and one embodiment of the present invention. As an example of the configuration, for example, as shown in FIG. 10B, an insulating layer 7 b as shown by a broken line is also continuous with the insulating layer 7 at a part of the end face of the side surface portion of the conductive substrate 1. By forming the insulating substrate, an insulating substrate having a configuration in which the insulating creepage distance between the conductive substrate 1 and the heat sink 8 is increased can be applied.
(B) However, in FIG. 10B, when the insulating layer is formed by spraying ceramic powder to the end surface of the side surface portion in addition to the first surface 1a of the conductive substrate 1, the conductive substrate 1 A sprayed film cannot be formed on the end face of the side surface simply by spraying the raw material powder in the direction facing the first surface 1a. For this reason, the raw material powder is sprayed along a direction orthogonal to the direction facing the first surface 1a of the conductive substrate 1 or in an oblique direction to form a sprayed film on the end surface of the side surface portion. In order to perform such spraying, a spraying apparatus having a complicated configuration in which spraying nozzles in a plurality of directions are combined is required.

In this respect, the configurations of the insulating substrate shown in the first and second reference embodiments and the embodiment of the present invention are both sprayed with the raw material powder in the direction facing the first surface 1a of the conductive substrate. Therefore, since it is possible to form a necessary sprayed film, it can be manufactured with a spraying apparatus having a simpler structure than the structure shown in FIG. 10B, which is more preferable in this respect.
(C) The insulating substrate 11C according to the embodiment of the present invention has a first surface with respect to the conductive plate-like member in a state before being separated into a plurality of conductive base materials as shown in FIG. 8, for example. A manufacturing method is also applicable in which an insulating layer is formed by spraying ceramic powder along a direction directly facing 101a, and then cut and separated into individual conductive substrates. On the other hand, the above configuration shown in FIG. 10B is obtained by spraying ceramic powder along a direction orthogonal to or oblique to the direction facing the first surface 1a of the conductive base material 1 to end the side surfaces. As a manufacturing method, an insulating layer is formed by spraying ceramic powder on a conductive plate-like member in a state before being separated into a plurality of conductive substrates. Later, it is difficult to apply a manufacturing method of cutting and separating into individual conductive substrates. In this regard, when considering the labor saving in the insulating layer forming process by thermal spraying, the configuration of the embodiment of the present invention enables an insulating substrate (conductive substrate with an insulating layer) to be manufactured at a lower cost. It is suitable.
[Configuration Example of Insulating Layer in Embodiment of the Present Invention]
(A) In the first and second reference embodiments described above and one embodiment of the present invention, an insulating substrate (conductivity with an insulating layer) provided with an insulating layer formed by spraying aluminum oxide powder as a ceramic powder. In the case where a semiconductor device is configured by attaching a heat sink to a semiconductor module having such an insulating substrate, the insulating layer needs to have high thermal conductivity and high insulation.
(B) As shown in a patent application (Japanese Patent Application No. 2009-266264) by the same applicant as the applicant of the present invention, first, the present inventor forms a method for forming an insulating layer on a conductive substrate. The reason why the thermal spraying method is focused on is that not only the formation cost of the layer is low, but also the pattern formation is easy. Specifically, the present inventor first formed a powder of aluminum oxide (Al ₂ O ₃ , alumina), which is a material suitable for an insulating layer, on a conductive substrate so as to be layered or film-formed by plasma spraying. did. Then, investigation was conducted as to whether or not the insulating properties and thermal conductivity desirable as a semiconductor module could be secured by using the sprayed insulating layer. As a result, the present inventor has found that the thermal conductivity of the insulating layer itself is approximately 3 to 4 W / m · K in many cases in which the final semiconductor module is manufactured using the aluminum oxide insulating layer formed by thermal spraying. I found out that there was a problem of staying in. Incidentally, the thermal conductivity of aluminum oxide (alumina sintered body) of the type produced by firing rather than thermal spraying is usually about 20 W / m · K. Nevertheless, as described above, the thermal sprayed insulating layer has a thermal conductivity of 3 to 4 W / m · K, that is, about 1/5 or less of the alumina sintered body. Therefore, even if a simple and low-cost thermal spraying method is used, it is difficult to realize a sufficiently small thermal resistance by using an insulating layer having such a thermal conductivity. This is because the thickness of the insulating layer must be reduced, and as a result, sufficient insulation cannot be ensured.
(C) In order to clarify the mechanism causing the above-described problems, the present inventor has further investigated and analyzed paying attention to the structure of the insulating layer formed by thermal spraying. First, attention was paid to the fact that the layer formed by thermal spraying generally contains many pores. Inclusion of pores is unavoidable as long as a spraying method is employed in which the raw material powder is heated to form a molten raw material powder jet and sprayed onto the object. Here, if it can be said that such pores are the cause of the above-described decrease in thermal conductivity, the decrease in thermal conductivity should be mitigated by adopting a layer forming condition that reduces the porosity. In practice, however, it has been found that the increase in porosity is related to the decrease in thermal conductivity to some extent, but pores alone cannot explain such a significant decrease in thermal conductivity. That is, it seems that the main cause of the above-mentioned decrease in thermal conductivity is other than the generation of pores.
(D) In response to the results of this investigation, the present inventors have come to the idea that the material itself is affected in some way in the insulating layer formed by thermal spraying. In particular, the inventor has been subjected to thermal and mechanical stress because the aluminum oxide powder is instantaneously melted and sprayed directly onto the substrate during thermal spraying, and this is the heat conduction of the material of the insulating layer. I guess this is the cause of the decline in the rate.
(E) Furthermore, the present inventor has intensively studied a method for increasing the value of the thermal conductivity of the insulating layer in consideration of the effect received when the insulating layer is formed by thermal spraying. As a result, the present inventor has found that the thermal conductivity of the insulating layer is increased by applying “heat treatment or annealing” (hereinafter also simply referred to as “heat treatment”) to the insulating layer formed by thermal spraying. I found it. More specifically, even if the insulating layer once has a thermal conductivity of 3 to 4 W / m · K by thermal spraying, the thermal conductivity is reduced to about 10 W / m · K by performing “heat treatment” after that. It was confirmed that it can be increased up to. If an insulating layer whose thermal conductivity is increased by performing a “heat treatment” on the insulating layer, the thermal resistance of the semiconductor module can be easily reduced.

For this reason, the insulating layer in the present invention is an insulating layer formed by spraying aluminum oxide powder on the first surface of the conductive base material and having increased thermal conductivity by “heat treatment”. preferable.
(F) According to the inventor's estimation, the following mechanism seems to act on the phenomenon that the thermal conductivity decreases due to thermal spraying and increases due to “heat treatment”. First, in the aluminum oxide layer as formed by the above-described thermal spraying, the crystal structure is changed as compared with the raw material powder. More specifically, the atomic arrangement of aluminum oxide changes from the hexagonal system, which is the structure of the original aluminum oxide powder (that is, corundum) before spraying, to the amorphous state or cubic or γ-alumina by spraying. doing. In this state, the thermal conductivity is a small value. The crystal structure of the thermally sprayed insulating layer becomes a hexagonal system by the subsequent “heat treatment”. In this hexagonal insulating layer, the thermal conductivity approaches the original value, and the thermal conductivity increases. Note that here, the crystal structure of the insulating layer is not necessarily hexagonal, and crystals that are hexagonal when the atomic arrangement is classified by type such as an amorphous state or a cubic with a long axial length. It is considered that there is a possibility that the thermal conductivity is increased by increasing the proportion of the structure, in particular, the proportion of α-alumina by “heat treatment”. That is, the present inventor has found that the thermal resistance of a semiconductor module using an insulating layer is reduced by making the crystal structure of the insulating layer hexagonal or increasing its proportion.

Therefore, the insulating layer in the present invention is preferably an insulating layer formed by spraying aluminum oxide powder on the first surface of the conductive base material and having a hexagonal crystal structure. (G) By these aspects, the thermal conductivity of the insulating layer of aluminum oxide is higher than that formed by thermal spraying (about 3 to 4 W / m · K), for example, 10 W / m · K or more. It becomes. When a semiconductor device is configured by attaching a heat sink to a semiconductor module having such an insulating layer in a heat dissipation path, good heat dissipation can be realized.
(H) As a specific configuration of the above-mentioned “heat treatment”, an insulating substrate in which an insulating layer is formed on one surface (first surface) of a conductive base material by spraying aluminum oxide powder, A “heat treatment step” is provided in which heating is performed by a furnace or a convection oven. This “heat treatment” is performed at any temperature between 500 ° C. and 1084 ° C. (melting point of copper) using air or nitrogen as an atmosphere. The above-mentioned temperature is a temperature at which the insulating layer reaches during the “heat treatment”. By this “heat treatment”, the atomic arrangement of the insulating layer becomes hexagonal and an insulating layer having an increased thermal conductivity can be obtained.

In the manufacturing method of the insulating substrates 11A, 11B, and 11C described in the first and second reference embodiments and the embodiment of the present invention, one of the conductive base materials is sprayed by spraying aluminum oxide powder. The “heat treatment step” may be provided as a treatment step after the insulating layer is formed on the surface (first surface).
[Modification]
The first and second reference embodiments described above and one embodiment of the present invention can be modified in various ways according to specific embodiments.
(A) In the present invention, as the insulating structure for improving the insulating property of the side face of the insulating substrate provided with the insulating layer formed by spraying ceramic powder on the first surface of the conductive substrate, “conductive” The “insulation creepage distance between the conductive base material and the metal member” is important, but “insulation layer thickness” is also important for ensuring sufficient withstand voltage characteristics of the insulating layer itself (bulk).

The thickness of the insulating layer formed on the first surface 1a of the conductive substrate is appropriately adjusted depending on the use of the semiconductor module and the semiconductor device. For example, in a power semiconductor module, a preferable value for the lower limit of the thickness of the insulating layer is 10 μm. In addition, a preferable value as the upper limit value of the thickness of the insulating layer is, for example, 500 μm in a semiconductor module used at a high voltage, and is 200 μm in other cases. More specifically, when the insulating layer is formed to have a thickness of 200 μm, it is possible to realize a power element semiconductor module that realizes both an AC breakdown voltage of 5 kV or more and a rated voltage of 1200 V. .
(B) In addition, the thermal conductivity of the insulating layer can typically be changed variously by changing the conditions of the “heat treatment”. For example, when the temperature of the “heat treatment” is increased in the case where the “heat treatment” is performed in the furnace, the thermal conductivity of the insulating layer generally increases. Even if the temperature is the same, if the time of the “heat treatment” is increased, the thermal conductivity is increased.

The ultimate temperature of the insulating layer by this “heat treatment” can be set to 1000 ° C., for example. In addition, it can be set to 1500 degreeC, for example. The “heat treatment” here is typically performed after the insulating layer is thermally sprayed on the conductive base material, but the embodiment of the present invention does not limit the order.
(C) The material, shape and manufacturing method of the conductive substrate are changed according to electrical requirements such as the amount of current flowing through the semiconductor circuit element, thermal requirements such as the amount of heat generated, and geometrical requirements such as weight and size. be able to. In determining the material of the conductive base material, the temperature of the “heat treatment” of the insulating layer can be taken into consideration. That is, although the above-mentioned embodiment demonstrated the electroconductive base material which uses a copper plate, an electroconductive base material is not limited to this. Typically, an aluminum substrate, an iron substrate, a molybdenum substrate, a substrate made of a copper alloy, or a substrate that is not plate-shaped may be used. The material of these base materials is selected in consideration of various conditions such as thermal properties and thermal expansion during production or operation.
(D) In each of the above-described embodiments, the conductive base material has been described using a plate-like shape having a square or rectangular shape, but the shape of the conductive base material is limited to those shapes. is not. A non-plate-shaped substrate may be a block-shaped or angle-shaped substrate. Furthermore, even if the shape of the conductive base material is limited to a plate shape, the planar shape can be various. For example, it is possible to adopt a shape in which individual areas of squares are connected to each other at the apex portion, or a shape having a rectangular outer shape and a hollow opening. And although such a base material may be cut out using the above-mentioned press processing, the processing method is not specifically limited, either. Moreover, the 1st surface and 2nd surface in an electroconductive base material are not necessarily limited to two main surfaces which prescribe | regulate the thickness of a plate-shaped board | substrate.
(E) In each of the above-described embodiments, the aspect of joining the semiconductor circuit element to the conductive substrate is not particularly limited. In addition to the above-described solder pellet bonding, any bonding technique such as cream solder bonding, bonding using a die bond resin material such as silver paste, bonding using a die bond film, or bonding using a conductive adhesive can be used.
(F) The above-described embodiments do not particularly limit the types of semiconductor circuit elements (chips or dies). For example, a semiconductor module on which a single circuit element is mounted can be formed by cutting out a circuit element such as a transistor element such as IGBT or MOS or a diode element from a semiconductor wafer. Moreover, even when a plurality of semiconductor circuit elements are mounted on a single piece of conductive base material as in the semiconductor module 21A shown in FIG. 1A, the types of semiconductor circuit elements can be arbitrarily combined. it can. For example, the same type of semiconductors can be connected in parallel, in series, or a combination thereof, and the current capacity can be set variously. As an example using different types of semiconductor elements, an IPM (intelligent power module) can be used. In other words, an IGBT for inverter use and a free-wheeling diode or freewheeling diode which is a semiconductor circuit element different from the IGBT can be mounted on a single piece of conductive substrate. As another example using different types of semiconductor elements, a small semiconductor module can be realized by mounting a diode for a converter and a transistor for an inverter on the same substrate.
(G) In each of the above-described embodiments, the sealing with the molding resin has been described. However, other sealing methods can be used. Specifically, for example, not only the resin to be solidified but also a sealing agent having fluidity such as silicone gel can be used.
(H) In each of the above-described embodiments, the insulating substrate provided with the insulating layer formed by spraying aluminum oxide powder as the ceramic powder has been described. However, the present invention applies thermal spraying of ceramic powder other than aluminum oxide. The present invention can also be applied to an insulating substrate provided with an insulating layer formed in this manner.

DESCRIPTION OF SYMBOLS 1,1A, 1B, 1C: Conductive base material 1a: 1st surface 1b: 2nd surface 1Ac: Tapered surface 1Bc, 1Cc: Notch part 2: Semiconductor circuit element 4: Bonding wire 5: Sealing agent (molding resin) )
6: Lead frame 7, 7A, 7Aa, 7Ab, 7B, 7C, 7Ca, 7Cb: Insulating layer 7C1, 7C1a, 7C1b: Insulating layer (sprayed layer)
8: Metal member (heat sink)
11, 11A, 11B, 11C: Insulating substrate (conductive substrate with insulating layer)
21, 21A, 21B, 21C: Semiconductor module 31, 31A, 31B, 31C: Semiconductor device 51: Ceramic insulating substrate 53: Ceramic substrate 54: Metal plate 55: Power semiconductor chip 56: Solder layer 57: Front circuit board 58: Back Circuit board 71: Raw material powder (aluminum oxide powder)
101C: Conductive plate member 101a: First surface 101b: Second surface 101Cc: Notch groove 107C, 107Ca, 107Cb: Insulating layer 107C1, 107C1a, 107C1b: Insulating layer (sprayed layer)
111C: Conductive plate member with insulating layer 201A, 201B: Electrode (copper adhesive tape)
202A, 202B: Electrode M of dielectric breakdown test apparatus: Mask θ: Inclination angle (taper angle) of taper surface 1Ac

Claims (10)

An insulating substrate comprising an insulating layer formed by spraying ceramic powder on a first surface of a conductive substrate having a first surface and a second surface,
A semiconductor device is configured by mounting at least one or more semiconductor circuit elements in direct or indirect contact with the second surface of the conductive substrate and attaching a metal member in close contact with the surface of the insulating layer. In the insulating substrate used for
The conductive substrate has a notch at a corner on the first surface side,
Also in this notch part, an insulating layer formed by spraying the ceramic powder is provided so as to be continuous with the insulating layer on the first surface,
A bottom surface parallel to the first surface is formed on the second surface side of the notch, and the insulating layer is formed by spraying the ceramic powder from a direction facing the bottom surface. Insulating substrate. The insulating substrate according to claim 1,
An aluminum oxide powder is used as the ceramic powder,
The insulating substrate is an insulating layer formed by spraying the aluminum oxide powder and having a thermal conductivity increased by heat treatment. The insulating substrate according to claim 1,
An aluminum oxide powder is used as the ceramic powder,
The insulating substrate is an insulating layer formed by spraying the aluminum oxide powder and having a hexagonal crystal structure. The insulating substrate according to any one of claims 1 to 3,
The insulating substrate has a thickness of 80 μm to 300 μm. An insulating substrate according to any one of claims 1 to 4,
A semiconductor module comprising: at least one semiconductor circuit element mounted in direct or indirect contact with the second surface of the conductive substrate. The semiconductor module according to claim 5,
Surfaces other than the first surface of the conductive base material are sealed with a sealing agent that is an insulating material together with a semiconductor circuit element mounted on the second surface,
A semiconductor module comprising an insulating surface that covers the conductive base material with the sealant and the insulating layer formed on the first surface. The semiconductor device according to claim 5, wherein a cooling metal member is attached in close contact with the surface of the insulating layer in the semiconductor module according to claim 5. A notch processing step of forming a notch at a corner on the first surface side of the conductive substrate having the first surface and the second surface;
After the notch processing step, an insulating layer forming step of forming an insulating layer on the first surface of the conductive base material and the notch portion by spraying ceramic powder;
After the insulating layer forming step, the insulating layer formed on the first surface is ground so that the surfaces of the insulating layer on the first surface and the insulating layer of the notch are aligned. When,
After the grinding step, at least one semiconductor circuit element is mounted in direct or indirect contact with the second surface of the conductive base material and the insulating layer formed on the first surface A semiconductor module manufacturing process for attaching a metal member in close contact with the surface,
In the notch processing step, a bottom surface parallel to the first surface is formed on the second surface side of the notch,
In the insulating layer forming step, the insulating layer is formed by spraying the ceramic powder from a direction facing the bottom surface. In the manufacturing method of the insulated substrate of Claim 8,
An aluminum oxide powder is used as the ceramic powder,
After the insulating layer forming step, the method includes a step of increasing the thermal conductivity of the insulating layer by heat-treating the insulating layer.
An insulating substrate manufacturing method characterized by the above. In the manufacturing method of the insulated substrate of Claim 8,
An aluminum oxide powder is used as the ceramic powder,
After the insulating layer forming step, a step of making the crystal structure of the insulating layer a hexagonal system is provided.
An insulating substrate manufacturing method characterized by the above.