JP7018756B2 - Power module board and power module - Google Patents

Description

The present invention relates to a power module substrate and a power module having a metal plate bonded to a ceramic substrate.

Conventionally, as a substrate for a power module used for a power module equipped with an electronic component such as an IGBT (Insulated Gate Bipolar Transistor), for example, a metal plate made of a metal material such as copper is joined as a circuit conductor to the surface of a ceramic substrate. A power module substrate is used.

An electronic component is mounted on a metal plate of a power module board to manufacture a power module. In order to improve the durability of the heat cycle, the outer peripheral end of the bonding layer for joining the metal plate and the ceramic substrate may be located outside or inside the lower end of the metal plate (see, for example, Patent Document 1). .).

Japanese Unexamined Patent Publication No. 10-326949

In recent years, the amount of heat generated by electronic components such as power semiconductor elements mounted on them has increased, and higher reliability is required for power modules. There is a demand for a power module substrate having a structure in which the possibility that the metal plate is peeled off from the ceramic substrate due to repeated thermal stress is further reduced.

The substrate for a power module according to one aspect of the present invention includes a ceramic substrate and a metal plate bonded to the surface of the ceramic substrate via a brazing material, and the thermal expansion coefficient of the brazing material is the metal. The brazing material is larger than the thermal expansion rate of the plate, and the brazing material is joined to the outer periphery of the metal plate with the metal plate, and is joined to the ceramic substrate inside the outer periphery of the metal plate.
The side surface of the plate is located inside the outer peripheral end portion on the opposite side of the ceramic substrate and has a portion including the inner peripheral end portion, with respect to the outer peripheral end portion on the metal plate side of the brazing material. The length at which the outer peripheral end portion on the ceramic substrate side is located inside is larger than the length at which the inner peripheral end portion is located inside the outer peripheral end portion on the side surface of the metal plate .

The power module according to one aspect of the present invention includes a power module substrate having the above configuration and electronic components mounted on the metal plate of the power module substrate.

According to the substrate for a power module according to the embodiment of the present invention, at the outer edge of the metal plate, the brazing material is joined to the outer periphery of the metal plate with the metal plate, and the ceramic substrate is from the outer periphery of the metal plate. Since they are joined on the inside, the possibility that the metal plate is peeled off from the ceramic substrate due to thermal stress can be reduced.

According to the power module of the embodiment of the present invention, the joining reliability is improved because of the above configuration.

(A) is a plan view showing an example of a power module substrate and an embodiment of a power module, and (b) is a cross-sectional view taken along the line BB of (a). It is sectional drawing which shows the example of the part A of FIG. 1 enlarged. (A) and (b) are sectional views showing another example of an embodiment of a power module. It is sectional drawing which shows the example of the main part of the board for a power module in an enlarged manner. It is sectional drawing which shows the other example of the main part of the board for a power module in an enlarged manner. It is sectional drawing which shows the other example of the main part of the board for a power module in an enlarged manner. It is sectional drawing which shows the other example of the main part of the board for a power module in an enlarged manner. It is sectional drawing which shows the other example of the main part of the board for a power module in an enlarged manner. It is sectional drawing which shows the other example of the main part of the board for a power module in an enlarged manner. It is sectional drawing which shows the other example of the main part of the board for a power module in an enlarged manner. It is sectional drawing which shows an example of the manufacturing method of the substrate for a power module in the order of a process.

The power module substrate and the power module according to the embodiment of the present invention will be described with reference to the drawings. It should be noted that the distinction between the upper and lower parts in the following description is for convenience, and does not limit the upper and lower parts when the power module board, the power module, and the like are actually used.

1 (a) is a plan view showing an example of an embodiment of a power module, and FIG. 1 (b) is a cross-sectional view taken along the line BB of FIG. 1 (a). Further, FIG. 2 is an enlarged cross-sectional view showing an example of part A in FIG. 1.

The power module substrate 10 includes a ceramic substrate 1 and a metal plate 2 bonded to the surface of the ceramic substrate 1 via a brazing material 3. The thermal expansion rate of the brazing material 3 is the thermal expansion of the metal plate 2. The brazing filler metal 3 is joined to the metal plate 2 up to the outer periphery of the metal plate 2, and is joined to the ceramic substrate 1 inside the outer periphery of the metal plate 2. In other words, at the outer edge of the metal plate 2, the brazing filler metal 3 is bonded to the metal plate 2, but not to the ceramic substrate 1. At the outer edge of the metal plate 2, there is a space between the metal plate 2 and the ceramic substrate 1 between the brazing material 3 bonded to the metal plate 2 and the brazing material 3 and the ceramic substrate 1.

When the power module substrate 10 is heated or cooled, thermal stress is mainly generated between the metal plate 2 and the ceramic substrate 1. Since the heat shrinkage of the metal plate 2 is large during cooling, the metal plate 2 warps so as to be concave, and the outer edge portion of the metal plate 2 is peeled off from the ceramic substrate 1. However, in the power module substrate 10 having the above configuration, since the metal plate 2 is not bonded to the ceramic substrate 1 up to the outer periphery thereof, the thermal stress is smaller than that in the case where the metal plate 2 is bonded to the outer periphery. Then, a brazing material 3 having a thermal expansion coefficient larger than that of the metal plate 2 is bonded to the outer edge portion of the lower surface of the metal plate 2 bonded to the upper surface of the ceramic substrate 1. Therefore, at the outer edge portion of the metal plate 2, the metal plate 2 behaves as if the metal plate 2 warps toward the brazing material 3 having a larger heat shrinkage than the metal plate 2. As a result, the behavior that the metal plate 2 is peeled off from the ceramic substrate 1 is suppressed. That is, the possibility that the metal plate 2 is peeled off from the ceramic substrate 1 due to a thermal stress load such as a heat cycle is reduced.

As shown in the example shown in FIG. 1, the power module 100 is basically composed of the power module substrate 10 as described above and the electronic components 11 mounted on the power module substrate 10. The electronic component 11 is mounted on the metal plate 2 of the power module substrate 10 and fixed by the bonding material 11a. According to such a power module 100, since the power module substrate 10 having the above configuration is provided, the reliability of the heat cycle and the like is improved.

3 (a) and 3 (b) are cross-sectional views showing another example of the embodiment of the power module. This is an example in which the power module 100 of the example shown in FIG. 1 is provided with an electronic component 11, a metal plate 2, a sealing resin 13 for covering the ceramic substrate 1, and the like. In the power module 101 of the example shown in FIG. 3A, the power module 100 of the example shown in FIG. 1 is covered with a sealing resin 13 from the upper surface to the outer peripheral portion of the lower surface, and the electronic component 11 is sealed. It is a thing. In the power module 102 of the example shown in FIG. 3B, the power module 100 of the example shown in FIG. 1 is arranged in the internal space of the housing 14 having an inner space, and the internal space is filled with the sealing resin 13. This is an example in which the electronic component 11 and the power module substrate 10 are sealed.

Such a sealing resin 13 also generally has a larger thermal expansion rate than the ceramic substrate 1. Therefore, the sealing resin 13 may also be peeled off from the ceramic substrate 1 due to a heat cycle or the like. In the power modules 101 and 102 including the power module substrate 10 having the above configuration, the sealing resin 13 is also bonded to the outer edge portion of the metal plate 2. Therefore, when the heat cycle is applied to the power modules 101 and 102, the outer edge portion of the metal plate 2 warps toward the brazing filler metal 3 side, that is, the ceramic substrate 1 side as described above. The behavior is such that the bonded resin 13 is pressed toward the ceramic substrate 1. This reduces the possibility that the sealing resin 13 will come off from the ceramic substrate 1. That is, the power modules 101 and 102 have improved sealing reliability. When the sealing resin 13 has entered the space between the brazing material 3 and the ceramic substrate 1 on the outer edge of the metal plate 2, it is sealed by the lower surface (the surface on the ceramic substrate 1 side) of the outer edge of the metal plate 2. Since the stop resin 13 is suppressed, the sealing reliability is further improved.

4 to 10 are enlarged cross-sectional views showing a main part of the power module substrate 10 similar to FIG. 2. The two-dot chain line in FIGS. 4 to 10 shows a perpendicular line to the surface (upper surface) of the ceramic substrate 1 in contact with the outermost end portion of the metal plate 2. The side surface of the metal plate 2 of the power module substrate 10 of the example shown in FIG. 2 is substantially perpendicular to the surface (upper surface) of the ceramic substrate 1 and is flat. On the other hand, the side surface of the metal plate 2 in the examples shown in FIGS. 4 to 10 has a portion located inside the outer peripheral end portion (upper end portion in FIGS. 4 to 10) opposite to the ceramic substrate 1. Have. In the example shown in FIGS. 4 and 9, the upper end of the side surface of the metal plate 2 is the outer peripheral end on the ceramic substrate 1 side (the lower end in FIGS. 4 and 9, and the same applies hereinafter in FIGS. 5 to 8 and 10). .) An inclined flat inclined surface located outside. The lower end is located inward with respect to the upper end by the length of the arrow shown in the figure. In the example shown in FIGS. 5 and 6, the side surface 2 is a concave surface (concave curved surface). In the example shown in FIG. 5, the positions of the upper end portion and the lower end portion of the metal plate 2 in the plane direction are the same, and the outermost end portions are the upper end portion and the lower end portion. On the other hand, in the example shown in FIG. 6, the upper end of the metal plate 2 is located inside the lower end, but the innermost bottom portion of the concave surface is located inside the upper end. In the examples shown in FIGS. 7, 8 and 10, the side surface 2 is concave from slightly below the upper end of the metal plate 2.

In this way, the side surface of the metal plate 2 can be a power module substrate 10 having a portion located inside the outer peripheral end portion on the opposite side of the ceramic substrate 1. With such a configuration, the sealing resin 13 enters the lower side (ceramic substrate 1 side) of the side surface of the metal plate 2, the sealing resin 13 is pressed by the side surface of the metal plate 2, and the metal plate 2 is also pressed. Since the bonding area between the metal and the sealing resin 13 is increased, the sealing resin 13 is less likely to be peeled off from the ceramic substrate 1, and the power modules 101 and 102 have higher sealing reliability. Further, such an effect can be obtained even if the sealing resin 13 does not enter the space between the brazing material 3 at the outer edge of the metal plate 2 and the ceramic substrate 1.

As in the examples shown in FIGS. 5 and 6, when the entire side surface of the metal plate 2 is concave, the bottom of the concave surface is located inside the lower end of the metal plate 2 (outer peripheral end on the ceramic substrate 1 side). is doing. Therefore, as compared with the case where the side surface of the metal plate 2 is an inclined surface, it is not necessary to project the upper end of the metal plate 2 to the outside from the lower end in order to provide a portion into which the sealing resin 13 enters. 1
Even if the maximum length into which the metal plate 3 is inserted (the length indicated by the arrow in the figure) is the same, if the side surface is concave, the metal plate 2 does not become unnecessarily large. The same applies to the case where the entire side surface is not concave and a part of the side surface in the thickness direction is concave, that is, the side surface has concave recesses, as in the examples shown in FIGS. 7, 8 and 10. Moreover, even if it is not a concave surface like these, it is the same as long as there is a concave surface. That is, the metal plate 2 can be assumed to have a recess on the side surface. As for the shape of the concave portion, if the concave surface (concave curved surface) as described above is used, the sealing resin 13 can easily enter, so that the above effect can be more reliably achieved.

As in the example shown in FIG. 5, when the entire side surface of the metal plate 2 is concave, the corner between the upper surface (the surface opposite to the ceramic substrate 1) and the side surface of the metal plate 2 (the corner of the upper end). ) Becomes an acute angle. If the distance between the adjacent metal plates 2 is small, when a large current is applied to the metal plates, a discharge may occur between the corners of the upper ends of the adjacent metal plates 2, resulting in poor insulation. On the other hand, in the example shown in FIG. 6, the entire side surface is concave, but the upper end of the metal plate 2 is located inside the lower end, and the distance between the corners of the upper ends is large between the adjacent metal plates 2. Therefore, the possibility that the above discharge occurs is reduced. In the example shown in FIG. 7, since the recess is provided on the ceramic substrate 1 side from the upper end of the metal plate 2, the corner of the upper end is not an acute angle. In this case, the concentration of the current on the upper end corner is suppressed as compared with the case where the upper end corner is an acute angle, so that the possibility of the discharge occurring is reduced. Further, in the example shown in FIG. 8, since the upper end corner is rounded, the possibility that the above discharge occurs is reduced. Since the possibility of electric discharge is reduced, the distance between the adjacent metal plates 2 can be reduced, so that the metal plates 2 which are wiring conductors can be arranged at high density on the ceramic substrate 1. , It can be a smaller power module substrate 10. This can be applied even when the side surface of the metal plate 2 is an inclined surface as in the example shown in FIG. 4, and the ceramic substrate 1 side is an inclined surface from the upper end on the side surface of the metal plate 2, or the example shown in FIG. You can round the top corners like this.

In the example shown in FIG. 10, the shape of the side surface of the metal plate 2 is the same as the example shown in FIG. 8, but the shape of the brazing filler metal 3 is different. Like this example. It can be assumed that the portion of the brazing material 3 on the metal plate 2 side protrudes outward from the outer periphery of the metal plate 2. When the power module substrate 10 has such a configuration, in the case of the power modules 101 and 102 including the sealing resin 13 covering the power module substrate 10, the protruding portion of the brazing material 3 bites into the sealing resin 13. Therefore, the sealing resin 13 is less likely to be peeled off from the ceramic substrate 1, and the power modules 101 and 102 have higher sealing reliability.

The ceramic substrate 1 is made of a ceramic sintered body, and is a substrate portion for fixing and supporting the metal plate 2. Further, the ceramic substrate 1 also functions as an insulating member for electrically insulating the plurality of metal plates 2 bonded to the surface of the ceramic substrate 1 from each other. It also functions as a heat transfer member that conducts heat between the upper and lower surfaces of the ceramic substrate 1. The size of the ceramic substrate 1 is appropriately set according to the application of the power module 100 and the like. For example. The thickness can be 0.25 mm to 1.0 mm, and the size in a plan view can be a rectangular shape having a side length of 10 mm to 200 mm.

Known materials can be used as the ceramic sintered body of the ceramic substrate 1, for example, an alumina (Al ₂ O ₃ ) sintered body, an aluminum nitride (Al N) sintered body, and a silicon nitride (Si ₃ N ₄ ). A sintered body or the like can be used. The ceramic substrate 1 can be manufactured by a known manufacturing method. For example, the ceramic substrate 1 can be manufactured by adding a sintering aid to a raw material powder such as alumina, forming the ceramic substrate into a substrate, and then firing the ceramic substrate 1.

The metal plate 2 is formed of a metal material such as copper or a copper alloy. In terms of electrical conduction and heat conduction, it is preferable to use pure copper of 99% or more, and a smaller oxygen content in the metal plate 2 is advantageous in improving the bonding strength between the bonding wire 12 and the metal plate 2. .. The size and shape of the metal plate 2 are also appropriately set according to the application of the power module 100 and the like, but for example. The thickness can be 0.1 mm to 1.0 mm.

In the power module substrate 10 of the example shown in FIG. 1, a metal plate 2 joined to the central portion of the upper surface of the ceramic substrate 1, a pair of metal plates 2 arranged and joined so as to sandwich the metal plate 2, and a pair of metal plates 2 joined to sandwich the metal plate 2. A metal plate 2 joined to the lower surface of the ceramic substrate 1 is provided. In this example, the metal plate 2 joined to the upper surface of the ceramic substrate 1 mainly functions as wiring for an electric circuit, and the metal plate 2 joined to the lower surface of the ceramic substrate 1 functions as a heat dissipation plate. The number, shape, arrangement, etc. of the metal plates 2 are not limited to this example.

The brazing filler metal 3 has a higher thermal expansion rate than the material of the metal plate 2, and is a silver-copper (Ag-Cu) -based active brazing filler metal containing at least one active metal material among, for example, titanium, hafnium, and zirconium. It is a material. As the Ag—Cu based brazing material, for example, B—Ag8 (JIS Z 3261-1985) can be used. The coefficient of thermal expansion of the B-Ag8 silver brazing material is larger than the coefficient of thermal expansion of copper of the metal plate 2.

The portion where the brazing filler metal 3 is joined to the metal plate 2 and not to the ceramic substrate 1 depends on the size of the metal plate 2, but for example, from the outer periphery of the surface of the metal plate 2 on the ceramic substrate 1 side. It can be in the range of about 0.05 mm to 1.0 mm.

The power module substrate 10 to which the brazing filler metal 3 is bonded to the metal plate 2 up to the outer periphery of the metal plate 2 and to the ceramic substrate 1 inside the outer periphery of the metal plate 2 is manufactured, for example, as follows. be able to. FIG. 11 is a cross-sectional view showing an example of a manufacturing method of the power module substrate 10 in the order of processes. In this example, an example is shown in which a power module substrate 10 having a configuration in which only one metal plate 2 is bonded to the upper surface of the ceramic substrate 1 is simply manufactured.

First, as shown in FIG. 11A, a film of the flow prevention material 24 is formed on the ceramic substrate 1. The shape of the flow prevention material 24 is a shape having an opening in the shape of a portion of the substrate 10 for a power module to be joined to the ceramic substrate 1 of the brazing material 3. The flow prevention material 24 does not disappear in the joining step described later, and can be easily removed after the metal plate 2 is joined to the ceramic substrate 1. For example, it is a paste of ceramic powder (for example, TiO ₂ , Al ₂ O ₃ , etc.) that is not sintered by heating in the joining process. A film of the flow prevention material 24 can be formed by applying the paste of the flow prevention material 24 to a predetermined shape on the upper surface of the ceramic substrate 1 by screen printing or the like and drying the paste.

Next, as shown in FIG. 11B, the brazing material paste 23 is applied so that the outer edge portion overlaps with the flow prevention material 24. The shape of the brazing paste 23 is the same as the shape of the metal plate 2. The brazing paste 23 can be produced by adding a solvent, a binder, or the like to the powder to be the brazing filler metal 3 (active brazing filler metal) and kneading the paste.

Next, as shown in FIG. 11C, the metal base plate 22 is placed on the brazing material paste 23 and heat-treated at, for example, about 830 ° C. in a vacuum state to obtain the metal base plate 22. Join to the upper surface of the ceramic substrate 1. At this time, in the portion where the flow prevention material 24 and the brazing material paste 23 overlap, the brazing material 3 is bonded only to the metal base plate 22 and not to the upper surface of the ceramic substrate 1.

Next, as shown in FIG. 11D, an etching mask 25 is formed on the upper surface of the metal base plate 22. The etching mask 25 is a portion corresponding to the metal plate 2 by a photolithography method, such as attaching a film-shaped resist material to the upper surface of the metal base plate 22 or applying a liquid resist material to the upper surface of the metal base plate 22. It can be formed by removing other than. It is also possible to print the liquid resin on the shape of the metal plate 2 to form the etching mask 25.

Next, as shown in FIG. 11 (e), the portion of the metal base plate 22 that is not covered with the etching mask 25 is removed by etching to form the metal plate 22 having a predetermined shape. At this time, the shape of the side surface of the metal plate 2 can be set depending on the etching conditions. By overetching, the side surface of the metal plate 2 can be made concave or the like.

Then, as shown in FIG. 11F, the etching mask 25 and the flow prevention material 24 are removed to form the power module substrate 10. When the flow prevention material 24 is removed, the brazing material 3 is bonded to the metal plate 2 and not to the upper surface of the ceramic substrate 1 at the outer edge portion of the metal plate 2, but is bonded to the upper surface of the brazing material 3 and the ceramic substrate 1. A space is formed between and. Since the flow prevention material 24 is like an agglomerate of ceramic powder, it can be easily removed by blasting or the like. For example, by performing this blasting process after removing the etching mask 25, the corner between the upper surface and the side surface of the metal plate 2 (the corner at the upper end) can be rounded.

In the example shown in FIG. 11, a metal base plate 22 having the same size as the ceramic substrate 1 is joined and then processed to the size of the metal plate 2 by etching. However, the metal base plate 22 is pressed or cut. It is also possible to perform mechanical processing such as etching or chemical processing such as etching to form a metal plate 2 having a predetermined shape in advance and bond it to the ceramic substrate 1. By the processing at this time, the side surface of the metal plate 2 can be processed into a predetermined shape. Further, instead of the ceramic substrate 1, a large metal base plate 22 is joined to a large ceramic substrate and etched to produce a multi-layer power module substrate in which a plurality of power module substrates 10 are integrated. However, by dividing this, a plurality of power module substrates 10 can be manufactured. Since the position accuracy of the arrangement of each power module board 10 (region) of the multi-cavity power module board is high, the electronic component 11 is mounted on the multi-cavity power module board without division. You can easily do that. As a result, the productivity of the mounting process can be increased, and the productivity of the power module 100 can be effectively increased.

Further, the brazing material 3 may not contain an active metal material. In this case, a base metal layer (not shown) for brazing may be provided at a predetermined portion on the upper surface of the ceramic substrate 1. The base metal layer is the surface of the ceramic substrate 1 as a metallized layer of a metal material containing a metal selected from, for example, silver, copper, indium, zinc, tin, titanium, zirconium, hafnium, niobium, molybdenum, osmium, rhenium, tungsten and the like. Can be formed in a predetermined position. In the above manufacturing method, a ceramic substrate 1 provided with a base metal layer slightly smaller than the size of the metal plate 2 in a plan view is prepared, a flow prevention material 24 is not provided, and a brazing metal paste 23 containing no active metal is used as a metal. By applying in a pattern similar to the size of the plate 2, the brazing material 3 is bonded to the metal plate 2 up to the outer periphery of the metal plate 2 and to the ceramic substrate 1 inside the outer periphery of the metal plate 2. ..

A metal film (not shown) can be provided on the exposed surfaces of the metal plate 2 and the brazing material 3. This metal film is a film for enhancing the bondability of the electronic component 11 to the metal plate 2 by the bonding material 11a. Therefore, it can be partially provided in the area where the electronic component 11 is mounted in the power modules 100, 101, 102. In this case, a recess can be provided in the mounting area of the metal plate 2 and a metal film can be provided on the bottom surface of the recess.

The metal film can be formed on the upper surface of the metal plate 2 bonded to the ceramic substrate 1 by, for example, a plating method. When the metal film is partially provided, in the plating process, if the area other than the region where the metal film is formed on the upper surface of the metal plate 2 is covered with a covering material (resist film) made of a resin material or the like, the metal film can be covered with a metal. It can be provided only on a part of the upper surface of the plate 2.

The surface of the metal film can be made of, for example, a silver layer or a gold layer. When such a metal film is arranged, it is possible to suppress oxidation of the portion of the upper surface of the metal plate 2 on which the electronic component 11 is mounted. Therefore, it is easy to join the electronic component 11 to the surface (upper surface) of the metal plate 2 via the joining material 11a and mount it, which is also advantageous for improving the electrical connection reliability. Since the surface of the metal film may be silver or gold, it may be a single layer of a silver layer or a gold layer, or may be composed of a plurality of layers having a silver layer or a gold layer as the outermost layer.

When the metal film is composed of a plurality of layers, a base layer having good bondability with the metal plate 2 can be provided, so that the bonding strength of the metal film to the metal plate 2 can be improved. Examples of the case where the metal film is composed of a plurality of layers include nickel / palladium / silver (Ni / Pd / Ag) and nickel / palladium / gold (Ni / Pd / Au) from the metal plate 2 side. Will be. The nickel layer has a function of improving the bonding strength of the metal film to the metal plate 2. The nickel layer has a property of having high adhesion strength to a material to be plated (metal plate 2) such as copper. Therefore, the metal film is firmly adhered to the upper surface of the metal plate 2 by the nickel layer. The palladium layer has a function of suppressing the diffusion of the nickel component of the nickel layer into the silver layer or the gold layer. Further, the palladium layer also has a function of improving the solder wettability when the electronic component 11 is mounted on the metal film via the solder, for example, when solder is used as the bonding material 11a. In this case, for example, even if a part of the silver layer or the gold layer is dissolved in the solder, the solder easily gets wet with the palladium layer. Therefore, the wettability of the solder can be improved.

Further, when the metal film includes a silver layer or a gold layer and a nickel layer arranged immediately below the silver layer, that is, only the nickel layer and the silver layer or the gold layer in which the metal film is sequentially adhered to the upper surface of the ceramic substrate 1. In the case of the above, since the diffusion of a metal such as copper from the metal plate 2 to the metal film can be suppressed, the thickness of the silver layer or the gold layer of the metal film can be suppressed, and the substrate 10 for the power module can be suppressed. The cost can be reduced.

When silver nanopaste is used as the bonding material 11a, the surface of the metal film can be a silver layer. By doing so, the silver nanoparticles and the metal film are easily bonded to each other, so that the silver nanopaste has high bondability to the metal plate 2 of the electronic component 11.

When the metal film is partially provided, the recess on the surface of the metal plate 2 is one size larger than the dimension of the electronic component 11 on which the dimension in a plan view is mounted, and is about the same size as the metal film. The depth of the recess is, for example, 2 μm to 20 μm. The recess can be formed by subjecting the surface of the metal plate 2 to mechanical processing such as blasting or chemical processing such as chemical etching. In either case, for example, a covering material (mask) having an opening at a position where a metal film is formed may be provided on the metal plate 2 and a recess may be formed by processing only the portion exposed from the opening. can. Therefore, by forming the recesses before forming the metal film by the plating method using the above-mentioned covering material, the recesses and the metal film can be efficiently formed.

Further, a plating layer such as nickel may be provided on the surface of the metal plate 2 bonded to the lower surface of the ceramic substrate 1. As a result, oxidation of the surface of the metal plate 2 can be suppressed. Further, when the metal plate 2 is bonded to the radiator with a heat conductive bonding material such as solder, the solder wettability can be improved and the thermal conductivity to the radiator can be improved.

By mounting the electronic component 11 on the power module board 10 as described above, the power module 100 as shown in FIG. 1 can be obtained. The power module 100 is used, for example, in an automobile or the like, and is used in various control units such as an ECU (engine control unit), a power assist handle, and a motor drive. The power module 100 is not limited to such an in-vehicle control unit, and is used, for example, in various other inverter control circuits, power control circuits, power conditioners, and the like.

In the power module 100 of the example shown in FIG. 1, one electronic component 11 is mounted on a metal plate 2 joined to the central portion of the surface (upper surface) of the ceramic substrate 1. The metal plate 2 arranged and joined so as to sandwich the metal plate 2 on which the electronic component 11 is mounted and the electronic component 11 are electrically connected by a bonding wire 12. The outer metal plate 2 functions as a terminal for connecting to an external electric circuit. Further, the heat generated in the electronic component 11 is transmitted to the metal plate 2 bonded to the lower surface of the ceramic substrate 1 via the metal plate 2 bonded to the upper surface of the ceramic substrate 1 and the metal plate 2 bonded to the lower surface of the ceramic substrate 1, and further dissipates to the outside. be able to. That is, the metal plate 2 joined to the lower surface of the ceramic substrate 1 functions as a heat sink. The number, size, mounting position, etc. of the electronic components 11 are not limited to the example shown in FIG.

The electronic component 11 is, for example, a power semiconductor, and is used for power control in various control units as described above. Examples thereof include transistors such as MOS-FETs (Metal Oxide Semiconductor-Field Effect Transistors) and IGBTs using Si, and power elements using SiC and GaN.

The electronic component 11 is joined to and fixed to the metal plate 2 of the power module substrate 10 by the joining material 11a. For the bonding material 11a, for example, solder or silver nanopaste can be used. When a metal film is partially provided on the surface of the metal plate 2, if the size of the electronic component 11 in a plan view is smaller than the size of the metal film, the bonding material 11a extends from the side surface of the electronic component 11 to the upper surface of the metal film. Since the fillet is formed, the bonding strength of the electronic component 11 to the metal plate 2 (metal film) can be increased. Further, since the surface of the metal film is covered with the bonding material 11a and is not exposed, the bonding property of the sealing resin 13 described later is improved.

The bonding wire 12 is a connecting member that electrically connects the terminal electrode (not shown) of the electronic component 11 and the metal plate 2. As the bonding wire 12, for example, one made of copper or aluminum can be used.

In the power module 101 of the example shown in FIG. 3A, the power module 100 of the example shown in FIG. 1 is covered with a sealing resin 13 from the upper surface to the outer peripheral portion of the lower surface, and the electronic component 11 is sealed. It is a thing. When a metal film is partially provided on the surface of the metal plate 2, the sealing resin 13 is bonded to the upper surface of the metal plate 2 on which the inactive silver layer or the metal film which is a gold layer is not formed. , The reliability of sealing the electronic component 11 by the resin layer 13 can be effectively improved. Further, the sealing resin 13 does not cover the main surface (lower surface) of the metal plate 2 bonded to the lower surface of the ceramic substrate 1. Therefore, since the metal plate 2 that functions as a heat radiating plate can be directly thermally connected to an external heat radiating body or the like, the power module 101 having excellent heat radiating properties can be obtained. Further, the metal plate 2 that functions as a terminal has a length that protrudes from the ceramic substrate 1 and also protrudes from the sealing resin 13. This makes it possible to easily electrically connect the metal plate 2 that functions as a terminal to an external electric circuit.

As the sealing resin 13, a thermosetting resin such as a silicone resin, an epoxy resin, or a phenol resin can be used from the viewpoint of thermal conductivity, insulating property, environmental resistance, and sealing property.

In the power module 102 of the example shown in FIG. 3B, the power module 100 of the example shown in FIG. 1 is arranged in the internal space of the housing 14 having an inner space, and the internal space is filled with the sealing resin 13. This is an example in which the electronic component 11 and the power module substrate 10 are sealed.

The housing 14 is composed of a frame body 15 and a heat radiating plate 16 that closes one opening of the frame body 15, and the space surrounded by the frame body 15 and the heat radiating plate 16 is an inner space. Further, it is provided with a lead terminal 17 that is led out from the inner space through the frame body 15 of the housing 14 to the outside. Then, the end portion of the lead terminal 17 in the internal space and the metal plate 2 of the power module substrate 10 are connected by a bonding wire 12. As a result, the electronic component 11 and the external electric circuit can be electrically connected to each other.

The frame 15 is made of a resin material, a metal material, or a mixed material thereof, and one of the openings is closed by the heat sink 16 to form an inner space for accommodating the power module substrate 10. The material used for the frame 15 is a metal material such as copper or aluminum or a resin such as polybutylene terephthalate (PBT) or polyphenylene sulfide (PPS) in terms of heat dissipation, heat resistance, environmental resistance and light weight. Materials can be used. Among these, it is desirable to use PBT resin from the viewpoint of easy availability. Further, it is preferable to add glass fiber to the PBT resin to obtain a fiber reinforced resin because the mechanical strength is increased.

The lead terminal 17 is a conductive terminal attached so as to penetrate the frame body 15 from the inner space and lead out to the outside. The end of the lead terminal 17 on the inner space side is electrically connected to the metal plate 2 of the power module board 10, and the end on the outer side is an external electric circuit (not shown) or a power supply device (not shown). ) Etc. are electrically connected. For the lead terminal 17, various metal materials used for the conductive terminal can be, for example, Cu and Cu alloy, Al and Al alloy, Fe and Fe alloy, stainless steel (SUS) and the like.

The heat radiating plate 16 is for radiating the heat generated by the electronic component 11 during operation to the outside of the power module 102. A high thermal conductive material such as Al, Cu, or Cu-W can be used for the heat sink 16. In particular, Al has higher thermal conductivity than a metal material as a general structural material such as Fe, and the heat generated in the electronic component 11 can be more efficiently dissipated to the outside of the power module 102, so that the electronic component 11 can be dissipated. Can be operated stably and normally. Further, Al is superior in that it is advantageous in reducing the cost of the power module 102 because it is easily available and inexpensive as compared with other high thermal conductive materials such as Cu or Cu-W.

The heat radiating plate 16 and the metal plate 2 of the power module substrate 10 are thermally connected by a heat-conducting bonding material (not shown). As the heat-conducting bonding material, a brazing material may be used for thermal connection and mechanically strong bonding, or a grease or the like may be used for thermal connection and mechanically relatively weak bonding may be performed. Further, it may be joined by the sealing resin 13 as described later.

The sealing resin 13 fills the inner space and seals and protects the electronic component 11 mounted on the power module substrate 10. The mechanical bonding between the power module substrate 10 and the heat sink 16 and the sealing of the inner space may be performed with the same sealing resin 13. In this case, the mechanically strong bonding between the power module substrate 10 and the heat sink 16 and the resin sealing can be performed in the same process.

In order to further improve the heat dissipation characteristics of the power module 102, a cooler is provided on the exposed surface of the heat dissipation plate 16 on the side opposite to the side to which the power module substrate 10 is bonded via the heat transfer bonding material 19. 18 may be joined. As the heat transferable bonding material 19, the same heat transferable bonding material as described above for connecting the heat radiating plate 16 and the metal plate 2 of the power module substrate 10 can be used. In the example shown in FIG. 3B, the cooler 18 shows a block body made of metal or the like provided with a flow path for passing a refrigerant such as water, but other cooling fins such as cooling fins may be used. good. Such a cooler 18 can also be applied to the power modules 100 and 101 of the example shown in FIG. 1 or FIG. 3A, and may be connected to the metal plate 2 of the power module substrate 10. In this case, only the flat plate-shaped one, that is, the heat sink 16 shown in FIG. 3B can be applied as the cooler 18.

1 ... Ceramic substrate 2 ... Metal plate 3 ... Wax material 10 ... Power module substrate 11 ... Electronic component 11a ... Bonding material 12 ... Bonding wire 13 ... Sealing Resin 14 ... Housing 15 ... Frame 16 ... Heat sink 17 ... Lead terminal 18 ... Cooler 19 ... Heat transfer bonding material 22 ... Metal base plate 23 ... Wax paste 24 ... Flow prevention material 25 ... Etching masks 100, 101, 102 ... Power module

Claims (5)

With a ceramic substrate
It is provided with a metal plate bonded to the surface of the ceramic substrate via a brazing material.
The thermal expansion coefficient of the brazing filler metal is larger than the thermal expansion coefficient of the metal plate.
The brazing material is joined to the metal plate up to the outer circumference of the metal plate, and is joined to the ceramic substrate inside the outer circumference of the metal plate .
The side surface of the metal plate is located inside the outer peripheral end portion on the opposite side of the ceramic substrate and has a portion including the inner peripheral end portion.
The length of the brazing material in which the outer peripheral end portion on the ceramic substrate side is located inside with respect to the outer peripheral end portion on the metal plate side is the inner circumference with respect to the outer peripheral end portion on the side surface of the metal plate. A board for power modules that is larger than the length with the ends located inside . The power module substrate according to claim 1 , wherein the metal plate has a recess on the side surface. The power module substrate according to claim 1 or 2 , wherein the brazing material has a portion on the metal plate side protruding outward from the outer periphery of the metal plate. The power module substrate according to any one of claims 1 to 3 .
A power module including electronic components mounted on the metal plate of the power module substrate. The power module according to claim 4 , further comprising a sealing resin covering the electronic component, the metal plate, and the ceramic substrate.

Images