JP2020068360A - Substrate for power module and power module - Google Patents

Abstract

To provide a substrate for a power module that is effective for improving connection reliability of an electronic component, and a power module.SOLUTION: A power module 100 comprises: a ceramic substrate 1; and metal plates 2 that are connected to a surface of the ceramic substrate 1. The metal plates 2 include a substrate for a power module 10 that has hollows in grain boundary parts in its surface, and electronic components 11 that are mounted on the substrate for a power module 10 and the metal plates 2.SELECTED DRAWING: Figure 1

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 power module substrate used in a power module in which electronic components such as an IGBT (Insulated Gate Bipolar Transistor) are mounted, for example, a metal plate made of a metal material such as copper is bonded as a circuit conductor to the surface of a ceramic substrate. A power module substrate is used.

  Electronic components are mounted on the metal plate of the power module substrate to manufacture a power module. Recently, a technique of using a sintered body of silver particles for joining an electronic component to a metal plate or the like has been proposed. Further, in order to prevent the oxide film from being formed on the surface of the metal plate and hindering the bonding, a technique of providing a metal film such as silver on the surface of the metal plate on which the electronic component is mounted has also been proposed ( See, for example, Patent Document 1. The connection reliability of the bonding wire is improved by providing the metal film on the part where the electronic component is mounted and not providing the metal film on the part where the bonding wire is connected (for example, Patent Document 1). 2).

JP, 2006-202938, A International publication 2015/114987 pamphlet

  In recent years, power modules are required to be small in size and have high output. As a result, electronic components generate high heat. Therefore, higher reliability is also required in connection between the electronic components and the metal plate of the power module substrate. Has been done. Therefore, it is necessary to increase the bonding strength of the bonding material for fixing the electronic component, the metal film between the bonding material and the metal plate, or the connection member such as the bonding wire to the surface of the metal plate.

  A power module substrate according to one aspect of the present invention includes a ceramic substrate and a metal plate bonded to a surface of the ceramic substrate, and the metal plate has a recess at a crystal grain boundary portion on the surface thereof. is doing.

  A power module according to one aspect of the present invention includes the power module substrate having the above configuration, and an electronic component mounted on the metal plate of the power module substrate.

  According to the power module substrate of the embodiment of the present invention, since the crystal grain boundary portion has a recess on the surface of the metal plate, the bonding strength of the bonding material, the connecting member or the metal film to the metal plate is high. Therefore, the power module substrate is effective for improving the connection reliability of electronic components.

  According to the power module of the embodiment of the present invention, the connection reliability of electronic components is improved because of the above-mentioned configuration.

(A) is a top view which shows an example of embodiment of a power module, (b) is sectional drawing in the BB line of (a). FIG. 1A is an enlarged cross-sectional view showing an example of a portion A in FIG. 1, and FIG. 1B is a plan view showing an example of a power module substrate in FIG. FIG. 1A is an enlarged cross-sectional view showing another example of the portion A in FIG. 1, and FIG. 1B is a plan view showing an example of a power module substrate in FIG. (A) is sectional drawing which expands and shows the principal part of the other example of embodiment of a power module, (b) is a top view which shows an example of the board for power modules in (a). (A) is sectional drawing which expands and shows the principal part of the other example of embodiment of a power module, (b) is a top view which shows an example of the board for power modules in (a). (A) is sectional drawing which expands and shows the principal part of the other example of embodiment of a power module, (b) is a top view which shows an example of the board for power modules in (a). (A) And (b) is sectional drawing which shows the other example of embodiment of a power module.

  A power module substrate and a power module of an 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 sides in the following description is for convenience, and does not limit the upper and lower sides when the power module substrate, the power module and the like are actually used.

  FIG. 1A is a plan view showing an example of an embodiment of the power module 100, and FIG. 1B is a sectional view taken along the line BB of FIG. 1A. Further, FIG. 2A is an enlarged cross-sectional view showing an example of the portion A in FIG. FIG. 2B is a plan view showing an example of the power module substrate 10 in FIG. 2A and shows a state in which the electronic component 11, the bonding material 11 a and the bonding wire 12 are removed. In FIG. 2B, the crystal grain boundary portion 2c is shaded in a dot shape for easy distinction, and the recess 2a of the crystal grain boundary portion 2c is not shaded.

  The power module substrate 10 includes a ceramic substrate 1 and a metal plate 2 bonded to the surface (main surface) of the ceramic substrate 1. As in the example shown in FIG. 2, the metal plate 2 is composed of a large number of metal crystal grains 2b, and a crystal grain boundary portion 2c which is a boundary between adjacent metal crystal grains 2b exists. The crystal grain boundary portion 2c is exposed on the surface of the metal plate 2. The metal plate 2 has a recess 2a in the crystal grain boundary portion 2c on its surface.

  According to the power module substrate 10 as described above, when the electronic component 11 such as a power semiconductor element is fixed to the surface of the metal plate 2 (21) with the bonding material 11a, as in the example shown in FIG. 2 (b). A part of the bonding material 11a will enter the recess 2a of the crystal grain boundary portion 2c exposed on the surface of the metal plate 2 (21). Therefore, the bonding strength between the bonding material 11a and the surface of the metal plate 2 (21) is improved, and the bonding strength of the electronic component 11 to the power module substrate 10 to the metal plate 2 (21) is high. Although not shown, part of the bonding wire 12, which is a connecting member connecting the electronic component 11 and the metal plate 2 (22), is also exposed at the surface of the metal plate 2 (22). It goes into the recess 2a of 2c. Therefore, the bonding strength between the bonding wire 12 and the surface of the metal plate 2 (22) is improved. Therefore, the power module substrate 10 is effective for improving the connection reliability of electronic components.

Since the recesses 2a are provided on the surface of the crystal grain boundary portion 2c, the recesses 2a are arranged so as to surround the metal crystal grains 2b and are evenly arranged on the surface of the metal plate 2. for that reason,
At the joining interface between the joining material 11a and the metal plate 2 (21), the portions where the joining material 11a enters the surface of the metal plate 2 (21) are evenly arranged, and the joining material 11a and the metal plate 2 (21) are joined together. Uneven strength is unlikely to occur.

  Furthermore, by utilizing the fact that the metal crystal grains 2b and the crystal grain boundary portions 2c have different chemical and mechanical characteristics, the recess 2a can be easily formed only in the crystal grain boundary portions 2c by etching, for example. it can.

  FIG. 3A is an enlarged sectional view showing another example of the portion A of FIG. FIG. 3B is a plan view showing an example of the power module substrate 10 in FIG. 3A, and shows a state in which the electronic component 11, the bonding material 11 a, and the bonding wire 12 are removed. In FIG. 3B, the crystal grain boundary portion 2c is shaded in a dot shape for easy distinction, and the bottom of the recess 2a of the crystal grain boundary portion 2c is shown by a broken line.

  In the example shown in FIG. 2, the recesses 2a of the crystal grain boundary portions 2c are scattered around the metal crystal grains 2b on the surface of the metal plate 2 (21), whereas in the example shown in FIG. In the surface of 2 (21), the entire surface of the crystal grain boundary portion 2c is recessed. Therefore, the recess 2a of the crystal grain boundary portion 2c has the same shape as the shape of the crystal grain boundary portion 2c and surrounds the metal crystal grain 2b. Thus, the recess 2a of the crystal grain boundary portion 2c can be formed in a net shape along the crystal grain boundary portion 2c in a plan view. When the recess 2a of the crystal grain boundary portion 2c has a mesh shape, the bonding material 11a enters into the recess 2a of the crystal grain boundary portion to form a honeycomb shape. Therefore, when thermal stress or the like is applied between the metal plate 2 (21) and the bonding material 11a, the portion that has entered into the recess 2a of the crystal grain boundary portion of the bonding material 11a is the metal plate 2 (21). It functions as a stronger anchor against stress in any direction in the surface direction (planar direction). Therefore, the bonding material 11a becomes more difficult to peel off from the metal plate 2 (21), and thus the bonding strength of the bonding material 11a to the metal plate 2 (21) can be further improved.

  FIG. 4A is an enlarged sectional view showing another example of the portion A of FIG. FIG. 4B is a plan view showing an example of the power module substrate 10 in FIG. 4A and shows a state in which the electronic component 11, the bonding material 11 a and the bonding wire 12 are removed. In FIG. 4B, the metal crystal grains 2b hidden under the metal coating 3 are indicated by broken lines.

  As in the example shown in FIG. 4, the power module substrate 10 can be provided with the metal film 3 on the surface of the metal plate 2. At this time, the metal film 3 covers the inner surface of the recess 2a of the crystal grain boundary portion 2c and is in close contact with the metal plate 2.

  In such a case, by interposing the metal coating 3 therebetween, the bonding strength of the bonding material 11a to the metal plate 2 can be increased. Further, the oxidation of the metal plate 2 can be prevented at other portions. Since the metal film 3 covers the inner surface of the recess 2a of the crystal grain boundary portion 2c and is in close contact with the metal plate 2, the metal film 3 and the metal plate 2 are compared to when the surface of the metal plate 2 is flat. The metal coating 3 is hard to peel off from the metal plate 2 because the bonding area with Even if the metal film 3 does not adhere to the entire inner surface of the recess 2a of the crystal grain boundary portion 2c (to the bottom), the bonding area becomes large. However, if there is a space between the metal film 3 and the bottom of the recess 2a, the gas in the space may expand due to heat and the metal film 3 may swell and be easily peeled off. Therefore, the metal film 3 which covers the entire inner surface of the recess 2a and adheres thereto can be provided. In addition, when the recess 2a of the crystal grain boundary portion has a mesh shape as described above, the metal coating 3 becomes more difficult to peel from the metal plate 2, and therefore the bonding strength of the metal coating 3 to the metal plate 2 is further improved. You can

FIG. 5 and FIG. 6 show enlarged main parts of another example of the power module 100, in which (a) is a cross-sectional view and (b) is an example of the power module substrate 10 in (a). FIG. 4 is a plan view showing a state in which the electronic component 11, the bonding material 11a and the bonding wire 12 are removed. In (b), the metal crystal grains 2b hidden under the metal coating 3 are indicated by broken lines.

  In the example shown in FIG. 4, the metal coating 3 is formed on the entire surface of the metal plate 2, for example, up to the part where the bonding material 11a is not bonded. On the other hand, the metal film 3 can be provided on a part of the surface of the metal plate 2 as in the examples shown in FIGS. For example, in the power module 100, the metal film 3 is provided on a portion where the electronic component 11 such as a power semiconductor element is mounted, that is, on a part of the surface of the metal plate 2 that functions as a circuit conductor. By providing the metal film 3 having the silver layer or the gold layer as the outermost layer, it is possible to suppress oxidation of the portion on the upper surface of the metal plate 2 (21) on which the electronic component 11 is mounted. Other than this, for example, by not providing the metal film 3 on the portion to which the bonding wire 12 is connected, the connection reliability of the bonding wire 12 can be improved.

  Further, in the example shown in FIGS. 5 and 6, the metal film 3 is provided on the bottom surface of the recess 2d provided on the surface of the metal plate 2. Therefore, when the power module substrate 10 is produced at the interface between the metal film 3 and the metal plate 2, that is, at the interface between the metal film 3 and the bottom surface of the recess 2d of the metal plate 2, for example, the metal film 3 is formed by a plating method. It has a structure in which the treatment liquid or the like during formation is unlikely to enter. Therefore, when the treatment liquid or the like enters the peripheral portion of the interface between the metal coating 3 and the metal plate 2, for example, the peripheral portion of the interface is corroded or the like, so that the bonding strength between the metal coating 3 and the metal plate 2 is increased. Is less likely to be reduced.

  As in the example shown in FIGS. 5 and 6, the thickness of the metal coating 3 can be smaller than the depth of the recess 2d. In such a case, wetting and spreading of the bonding material 11a from the metal coating 3 to the surface of the metal plate 2 can be suppressed. Therefore, when two electronic components 11 are mounted on one metal plate 2 as in the example shown in FIG. 1, a short circuit does not occur even if the two electronic components 11 are close to each other. Can be converted.

  In the example shown in FIG. 6, the metal coating 3 completely fills the recess 2a of the crystal grain boundary portion 2c, and the surface thereof is substantially flat. On the other hand, the thickness of the metal coating 3 in the example shown in FIG. 5 is smaller than the thickness of the metal coating 3 in the example shown in FIG. 6, smaller than the depth of the recess 2a of the crystal grain boundary portion 2c, and 1 / of the opening width. Less than 2 Therefore, the surface of the metal coating 3 in the example shown in FIG. 5 has a shape that follows the shape of the bottom surface of the recess 2d of the metal plate 2, and is recessed along the recess 2a at the upper portion of the recess 2a of the crystal grain boundary portion. . This also applies to the example shown in FIG. In this way, the surface of the metal coating 3 can be recessed in the upper part of the recess 2a of the crystal grain boundary portion. In other words, the metal coating 3 has a recess 3a on its surface that corresponds to the recess 2a of the metal grain boundary portion. In such a case, since the bonding material 11a enters into the recess 3a of the metal coating 3 and is bonded thereto, the bonding strength between the bonding material 11a and the metal coating 3 is improved, so that the electronic component 11 and the power module substrate. It is possible to more firmly join the No. 10 and.

  As in the example shown in FIG. 1, the power module 100 basically includes a power module substrate 10 as described above and an electronic component 11 mounted on the metal plate 2 (21) of the power module substrate 10. It is configured. According to such a power module 100, since the power module substrate 10 having the above-described configuration is provided, the bonding reliability of the electronic component 11 is improved.

The ceramic substrate 1 is made of a ceramics sintered body and is a base 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. Also,
It also functions as a heat transfer member that conducts heat between the upper and lower surfaces of the ceramic substrate 1.

A known material can be used as the ceramics sintered body of the ceramic substrate 1, and examples thereof include an alumina (Al ₂ O ₃ ) sintered body, an aluminum nitride (AlN) 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, shaping the substrate into a substrate shape, and then firing the substrate.

  The metal plate 2 is formed of a metal material such as copper or a copper alloy. From the viewpoint of electric conduction and heat conduction, it is preferable to use pure copper of 99% or more, and it is advantageous that the oxygen content in the metal plate 2 is small in terms of improving the bonding strength between the bonding wire 12 and the metal plate 2. .

  In the power module substrate 10 of the example shown in FIG. 1, the metal plate 2 (21) bonded to the central portion of the front surface (upper surface) of the ceramic substrate 1 is arranged so as to sandwich the metal plate 2 (21) and bonded. There are provided a total of four pairs of metal plates 2 (22) and a metal plate 2 (23) bonded to the lower surface of the ceramic substrate 1. In this example, the metal plate 2 bonded to the upper surface of the ceramic substrate 1 mainly functions as wiring of an electric circuit, and the metal plate 2 bonded 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 metal plate 2 is joined, that is, brazed, to the ceramic substrate 1 by, for example, an Ag—Cu-based brazing material (not shown) containing at least one active metal material selected from titanium, hafnium, and zirconium. The brazing material may not contain an active metal material. In this case, a base metal layer (not shown) for brazing may be provided on a predetermined portion of the upper surface of the ceramic substrate 1. The underlying metal layer is, for example, a metallized layer of a metal material containing a metal selected from silver, copper, indium, zinc, tin, titanium, zirconium, hafnium, niobium, molybdenum, osmium, rhenium, tungsten, etc. Can be formed at a predetermined position.

  The metal plate 2 may be preliminarily processed into a predetermined shape by punching or the like, and may be brazed. Alternatively, a metal base plate having the same size as the ceramic substrate 1 may be brazed to the ceramic substrate 1 and then etched. You may process it into the metal plate 2 of a predetermined shape. Brazing is performed by applying a brazing material paste containing the brazing material to a ceramic substrate, placing a metal plate 2 (metal base plate) on the brazing material paste, and heating. The brazing material paste at this time can be applied by screen printing or the like, but the brazing material paste may be applied to the entire surface of the ceramic substrate 1 or may be applied in a predetermined shape. When applying it on the entire surface of the ceramic substrate 1, after brazing the metal plate 2 (metal base plate), unnecessary portions between the metal plates 2 may be removed by etching or the like.

  The recess 2d on the surface of the metal plate 2 (21) when the metal film 3 is partially provided has a size in plan view that is slightly larger than the size of the electronic component 11 to be mounted. The depth of the recess 2d is, for example, 2 μm to 20 μm. The recess 2d 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 any case, for example, a coating material (resist film) having an opening at a position where the metal film 3 is formed is provided on the metal plate 2, and only the portion exposed from the opening is processed to form the recess 2d. can do. When the recess 2d is formed by etching, the same coating material can be used to continuously form the metal film 3.

Specifically, the recess 2d can be formed in the metal plate 2 as follows, for example. First, a coating film having an opening is formed on the surface of the metal plate 2 bonded to the ceramic substrate 1.
The coating film may be formed by applying a liquid resist material on the surface of the metal plate 2 and drying it, or by attaching a dry film resist. The opening of the resist film can be performed by exposure and development. Alternatively, a liquid coating material may be printed into a shape having an opening by screen printing to form a coating film. Next, also as a pretreatment for plating, the oxide film on the surface of the metal plate 2 exposed in the opening of the resist film is removed with an acidic aqueous solution of sulfuric acid, hydrochloric acid, hydroxylammonium chloride or the like, and degreasing is performed with alkali. do. Then, the surface of the metal plate 2 is etched with an etching solution such as sodium persulfate or ammonium persulfate to form the recess 2d. The depth of the recess 2d can be adjusted by the concentration of the etching solution, the etching time, and the like.

  The depression 2a of the crystal grain boundary portion 2c on the surface of the metal plate 2 can be formed by using the same etching solution as the etching for forming the depression 2d. When the metal film 3 is partially provided and the recess 2d is formed, it can be formed simultaneously with the formation of the recess 2d, for example. By adjusting the etching conditions such as the type and concentration of the etching liquid and the etching time, the crystal grain boundary portion 2c can be etched deeper than the metal crystal grain 2b. Alternatively, after forming the recess 2d on the surface of the metal plate 2, the recess 2a of the crystal grain boundary portion 2c is formed by etching the crystal grain boundary portion with a relatively weak etching solution such as sodium persulfate or ammonium persulfate. You can

  It is difficult to form a fine net-like recess on the bottom surface of the recess 2d of the metal plate 2 by cutting because the recess 2d is small. Even if polishing or blasting is performed, it is possible to form an uneven surface having point-like depressions on the bottom surface of the recess 2d, but it is difficult to form fine mesh-like depressions on the bottom surface of the small recess 2d.

  Since the recess 2a of the crystal grain boundary portion 2c has a mesh shape, the shape of the portion where the metal coating 3 enters the recess 2a of the crystal grain boundary portion becomes a wall shape, and the portion of the joining material 11a that enters the recess 3a of the metal coating 3 is formed. The shape is also wall-like. Since the part that enters the recess 2a of the grain boundary part or the recess 3a of the metal film 3 and functions as an anchor is wall-shaped, it functions more effectively than when the part that functions as an anchor is dot-shaped. Improves the bonding strength. The mesh-shaped recess 2a on the bottom surface of the relatively small recess 2d can be formed easily and at low cost by the above-described etching. The depressions 2a of the crystal grain boundary portion 2c and the depressions 3a of the metal coating 3 may have a net shape as a whole, and may have a portion divided in the middle.

  The recess 2a of the crystal grain boundary portion on the surface of the metal plate 2 has, for example, an opening width of about 3 μm to 10 μm and a depth of 2 μm to 20 μm from the bottom surface of the recess 2d. The shape and size of the mesh of the depressions 2a in the crystal grain boundary portion are due to the shape and size of the metal crystal grains 2b exposed on the bottom surface of the recess 2d of the metal plate 2, and the shape is polygonal and the maximum length is For example, it is 100 μm to 600 μm. The maximum length is the maximum length of the outer dimensions of the polygon, and is the diagonal length in the case of a rectangular shape, for example. The depression 3a of the metal coating 3 at this time has, for example, an opening width of about 1 μm to 10 μm and a depth of 1 μm to 20 μm from the bottom surface of the depression 2d.

The metal film 3 can be formed on the surface of the metal plate 2 joined to the ceramic substrate 1 by, for example, a plating method. When the metal coating 3 is provided on a part of the surface of the metal plate 2, in the plating step, a region other than the region where the metal coating 3 is formed on the upper surface of the metal plate 2 is covered with a coating material (resist film) made of a resin material or the like. If so, the metal film 3 can be provided only on a part of the upper surface of the metal plate 2. In this case, the coating material is removed by mechanical or chemical means after the plating process. Mechanical removal is a method of peeling off the resin material with a jig or the like, and chemical removal is a method of removing with a remover such as an organic solvent or an organic acid. Alternatively, the metal plate 3 may be formed on the entire upper surface of the metal plate 2, the region on which the electronic component 11 is mounted is covered with a coating material, and the metal film 3 in the other regions may be removed by etching. The metal coating 3 can be partially provided on the upper surface of the metal layer 2. By forming the metal coating 3 after forming the recess 2d using the above-mentioned coating material, the recess 2d and the metal coating 3 can be efficiently formed.

  It is also possible to bond a metal base plate that is as large as the ceramic substrate 1 to the ceramic substrate 1, form a metal film 3 at a predetermined position by electrolytic plating, and then form a metal plate 2 having a predetermined shape by etching.

  The metal film 3 is, for example, a film of a metal such as nickel (Ni), gold (Au), and silver (Ag), and is a plating film as described above.

  The surface of the metal coating 3 may be composed of a silver layer or a gold layer. When the metal film 3 having a silver layer or a gold layer as the outermost layer is arranged on a portion of the upper surface of the metal plate 2 on which the electronic component 11 is mounted, a portion of the upper surface of the metal plate 2 on which the electronic component 11 is mounted is mounted. Oxidation and the like can be suppressed. Therefore, it is easy to bond and mount the electronic component 11 on the surface (upper surface) of the metal plate 2 (21) through the bonding material 11a, which is also advantageous for improving the electrical connection reliability. Since the surface of the metal film 3 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 coating 3 is a silver layer or a gold layer, that is, when the metal coating 3 is composed of only a silver layer or a gold layer, the number of plating, etching and heat treatment steps can be reduced in the step of forming the metal coating 3. . Therefore, it is possible to prevent the mechanical strength of the ceramic substrate 1 and the metal coating 3 from being lowered by the removing agent when removing the coating material, and to reduce the cost of the power module substrate 10 by reducing the number of steps.

  When the metal coating 3 is composed of a plurality of layers, it is possible to provide an underlayer having a good bonding property with the metal plate 2, so that the bonding strength of the metal coating 3 to the metal plate 2 can be improved. Examples of the case where the metal film 3 is composed of a plurality of layers include, for example, nickel / palladium / silver (Ni / Pd / Ag) and nickel / palladium / gold (Ni / Pd / Au) from the metal plate 2 side. can give. The nickel layer has a function of improving the bonding strength of the metal film 3 to the metal plate 2. The nickel layer has a high adhesive strength with respect to the material to be plated (metal plate 2) such as copper. Therefore, the metal film 3 is firmly adhered to the upper surface of the metal plate 2 by the nickel layer. The palladium layer has a function of suppressing diffusion of the nickel component of the nickel layer into the silver layer or the gold layer. The palladium layer also has a function of improving the solder wettability when the electronic component 11 is mounted on the metal film 3 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 palladium layer easily wets the solder. Therefore, the wettability of the solder can be improved.

  In addition, when the metal coating 3 includes a silver layer or a gold layer and a nickel layer disposed immediately below it, that is, the metal coating 3 is a nickel layer and a silver layer or a gold layer sequentially deposited on the upper surface of the ceramic substrate 1. When it is composed of only layers, diffusion of metal such as copper from the metal plate 2 to the metal coating 3 can be suppressed. Thereby, the thickness of the silver layer or the gold layer of the metal coating 3 can be suppressed, and the cost of the power module substrate 10 can be reduced.

  When silver nanopaste is used as the bonding material 11a, the surface of the metal coating 3 can be a silver layer. By doing so, the silver nanoparticles and the metal film 3 are easily bonded, so that the bondability of the electronic component 11 to the metal plate 2 by the silver nanopaste becomes high.

When the metal film 3 has a three-layer structure of Ni / Pd / Ag as described above, each layer can be formed as follows. The silver layer is formed, for example, by electroplating a metal plate 2 on which a nickel layer and a palladium layer are adhered at a predetermined current density and time in a cyan-based electrosilver plating solution containing silver cyanide as a main component. Can be formed. The formed silver layer is a so-called pure silver layer containing, for example, 99.99 mass% or more of silver. The silver layer may be directly applied to the upper surface of the metal plate 2 as in the above-mentioned example. The nickel layer can be formed by electroplating the metal plate 2 at a predetermined current density and time in a nickel plating solution such as a Watt bath containing nickel sulfate as a main component. The formed nickel layer is a metal layer containing nickel as a main component and a metal component such as cobalt. The palladium layer can be formed, for example, by subjecting the metal plate 2 on which the nickel layer has been deposited to electroplating at a predetermined current density and time in a palladium plating solution containing a palladium ammine complex as a main component. . The formed palladium layer is a so-called pure palladium layer containing, for example, 99.99% by mass or more of palladium.

  As a method for forming the metal film 3, for example, electroless plating method other than the above-described electroplating (electrolytic plating method) can be mentioned. However, the recess 2a of the crystal grain boundary portion is formed on the bottom surface of the recess 2d of the metal plate 2. Therefore, the electrolytic plating method is more effective when the metal coating 3 is adhered to the inner surface of the recess 2a of the crystal grain boundary portion so as to be adhered thereto. In the case of the electroless plating method, depending on the opening width and the depth of the recess 2a in the crystal grain boundary portion, the opening of the recess 2a in the crystal grain boundary portion is closed with the metal film 3 as compared with the electrolytic plating method. This is because the flakes easily form a space between the metal coating 3 and the bottom of the recess 2a in the crystal grain boundary portion. Such a space is a part where the metal film 3 and the metal plate 2 are not bonded and has a low bonding strength, and the gas in the space expands due to heating, and the metal film 3 expands. The bonding strength may be reduced.

  Further, a plating layer of nickel or the like may be provided on the surface of the metal plate 2 (23) joined to the lower surface of the ceramic substrate 1. Thereby, the oxidation of the surface of the metal plate 2 (23) can be suppressed. In addition, when the metal plate 2 (23) is bonded to the heat radiator with a heat conductive bonding material such as solder, the solder wettability can be improved, and the heat conductivity to the heat radiator can be improved.

By mounting the electronic component 11 on the power module substrate 10 as described above, a power module 100 such as the example shown in FIG. 1 is 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 steering wheel, and a motor drive. The power module 100 is not limited to such a vehicle-mounted control unit, but is used for other various inverter control circuits, power control circuits, power conditioners, and the like.

  In the power module 100 of the example shown in FIG. 1, two metal coatings 3 are provided at intervals on a metal plate 2 (21) bonded to the central portion of the surface (upper surface) of the ceramic substrate 1. One electronic component 11 is mounted on each of the two metal films 3. The metal plate 2 (22), which is arranged and bonded so as to sandwich the metal plate 2 (21) on which the electronic component 11 is mounted, and the electronic component 11 are electrically connected by the bonding wire 12. The outer metal plate 2 (22) 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 (21) bonded to the upper surface of the ceramic substrate 1 and the metal plate 2 (23) bonded to the lower surface of the ceramic substrate 1 via the ceramic substrate 1. Further, heat can be dissipated to the outside. That is, the metal plate 2 (23) bonded to the lower surface of the ceramic substrate 1 functions as a heat dissipation plate. The number, size and mounting position 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 the above various control units. For example, a transistor such as a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor) or an IGBT using Si, or Si
A power element using C or GaN can be given.

  The electronic component 11 is bonded and fixed on the metal film 3 provided on the metal plate 2 of the power module substrate 10 by the bonding material 11a. As the bonding material 11a, for example, solder or silver nano paste can be used. If the size of the bonding material 11a in plan view is larger than the size of the electronic component 11, a fillet of the bonding material 11a is formed from the side surface of the electronic component 11 to the upper surface of the metal plate 2 (metal coating 3). The bonding strength of 11 to the metal plate 2 (metal coating 3) can be increased. When the metal film 3 is provided, the size of the metal film 3 in plan view is made larger than the size of the electronic component 11. At this time, since the surface of the metal film 3 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 connection member that electrically connects a terminal electrode (not shown) of the electronic component 11 and the metal plate 2 (22). As the bonding wire 12, for example, one made of copper or aluminum can be used.

  FIG. 7A and FIG. 7B are sectional views showing another example of the embodiment of the power module. In the power module 100 of the example shown in FIG. 1, the metal film 3 is formed only on the region of the metal plate 2 (21) of the power module substrate 10 on which the electronic component 11 is mounted, and sealing is performed. This is an example including a resin or the like.

  In the power module 101 of the example shown in FIG. 7A, the power module 100 in which the electronic component 11 is mounted on the power module substrate 10 as in the example shown in FIG. 1 is sealed from the upper surface to the outer peripheral portion of the lower surface. The electronic component 11 is covered with the resin 13 and sealed. Since the sealing resin 13 is bonded to the upper surface or the like of the metal plate 2 on which the metal coating 3 which is an inactive silver layer or gold layer is not formed, the reliability of sealing the electronic component 11 by the sealing resin 13 is high. Can be effectively improved. Further, the sealing resin 13 does not cover the main surface (lower surface) of the metal plate 2 (23) joined to the lower surface of the ceramic substrate 1. Therefore, the metal plate 2 (23) functioning as a heat dissipation plate can be directly thermally connected to an external heat dissipation member or the like, so that the power module 101 having excellent heat dissipation can be obtained. Further, the metal plate 2 (22) functioning as a terminal has a length protruding from the ceramic substrate 1 and also protruding from the sealing resin 13. As a result, it is possible to easily electrically connect the metal plate 2 (22) functioning as a terminal to an external electric circuit.

  A thermosetting resin such as a silicone resin, an epoxy resin, or a phenol resin can be used for the sealing resin 13 in terms of thermal conductivity, insulation, environment resistance, and sealing property.

  In the power module 102 of the example shown in FIG. 7B, the power module 100 of the example shown in FIG. 1 is arranged in the internal space of the housing 14 having an internal space, and the internal space is filled with the sealing resin 13. In this example, the electronic component 11 and the power module substrate 10 are sealed.

  The housing 14 includes a frame body 15 and a heat dissipation plate 16 that closes one opening of the frame body 15. The space surrounded by the frame body 15 and the heat dissipation plate 16 is an inner space. In addition, a lead terminal 17 is provided that extends from the inner space to the outside through the frame body 15 of the housing 14. The end of the lead terminal 17 in the internal space is connected to the metal plate 2 (22) of the power module substrate 10 by the bonding wire 12. As a result, the electronic component 11 and the external electric circuit can be electrically connected.

The frame 15 is made of a resin material, a metal material, or a mixed material thereof, and one opening is closed by the heat dissipation plate 16 to form an inner space for housing the power module substrate 10. As a material used for the frame body 15, in terms of heat dissipation, heat resistance, environment resistance and light weight,
A metal material such as copper or aluminum or a resin material such as polybutyl terephthalate (PBT) or polyphenylene sulfite (PPS) can be used. Among these, it is preferable to use the PBT resin from the viewpoint of easy availability. Further, it is preferable to add glass fibers to the PBT resin to obtain a fiber reinforced resin because the mechanical strength increases.

  The lead terminal 17 is a conductive terminal attached so as to penetrate the frame 15 from the inner space and lead out to the outside. The inner space side end of the lead terminal 17 is electrically connected to the metal plate 2 (22) of the power module substrate 10, and the outer side end is an external electric circuit (not shown) or a power supply device (not shown). (Not shown) and the like. As various metal materials used for the conductive terminals of the lead terminal 17, for example, Cu and Cu alloys, Al and Al alloys, Fe and Fe alloys, and stainless steel (SUS) can be used.

  The heat dissipation plate 16 is for dissipating the heat generated in the electronic component 11 during operation to the outside of the power module 102. A high heat conductive material such as Al, Cu, or Cu-W can be used for the heat dissipation plate 16. In particular, Al has a higher thermal conductivity than a metal material as a general structural material such as Fe, and can dissipate the heat generated in the electronic component 11 to the outside of the power module 102 more efficiently. Can be operated stably and normally. In addition, Al is superior in that it is easy to obtain and inexpensive as compared with other high thermal conductivity materials such as Cu or Cu—W, and thus is advantageous in reducing the cost of the power module 102.

  The heat dissipation plate 16 and the metal plate 2 (23) of the power module substrate 10 are thermally connected by a heat conductive bonding material (not shown). As the heat conductive bonding material, a brazing material may be used for the thermal connection and mechanically strong connection, or grease may be used for the thermal connection, and the mechanical connection may be relatively weak. Further, they 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. Mechanical bonding between the power module substrate 10 and the heat dissipation plate 16 and sealing of the inner space may be performed with the same sealing resin 13. In this case, mechanical and strong joining of the power module substrate 10 and the heat dissipation plate 16 and resin sealing can be performed in the same step.

  In order to further improve the heat dissipation characteristics of the power module 102, the cooler is provided on the exposed surface of the heat dissipation plate 16 opposite to the side to which the power module substrate 10 is bonded, with the heat conductive bonding material 19 interposed therebetween. 18 may be joined. As the heat conductive bonding material 19, the same heat conductive bonding material as described above that connects the heat dissipation plate 16 and the metal plate 2 (23) of the power module substrate 10 can be used. In the example shown in FIG. 7B, the cooler 18 has a block body made of metal or the like provided with a flow path for allowing a coolant such as water to pass therethrough. However, other than this, for example, a cooling fin 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. 7B, and can be connected to the metal plate 2 (23) of the power module substrate 10. . In this case, a flat plate, that is, only the heat dissipation plate 16 shown in FIG. 7B can be applied as the cooler 18.

  The power module substrate 10 can also be manufactured by preparing a multi-cavity power module substrate and dividing it. Since the multi-cavity power module substrate has a high positional accuracy of the arrangement of the respective multi-cavity power module substrates 10 (regions), the electronic component 11 is mounted on the multi-cavity power module substrate without dividing the substrate. It can be done easily. As a result, the productivity of the mounting process can be increased, and the productivity of the power module 100 can be effectively increased.

DESCRIPTION OF SYMBOLS 1 ... Ceramic substrate 2 (21, 22, 23) ... Metal plate 2a ... Recess of crystal grain boundary portion 2b ... Metal crystal grain 2c ... Crystal grain boundary portion 2d ... Recess 3・ ・ ・ Metal coating 3a ・ ・ ・ Dent of metal coating 10 ・ ・ ・ Power module substrate 11 ・ ・ ・ Electronic component 11a ・ ・ ・ Bonding material 12 ・ ・ ・ Bonding wire 13 ・ ・ ・ Sealing resin 14 ・ ・ ・Housing 15 ... Frame 16 ... Heat dissipation plate 17 ... Lead terminal 18 ... Cooler 19 ... Heat conductive bonding material 100, 101, 102 ... Power module

Claims (6)

A ceramic substrate,
A metal plate bonded to the surface of the ceramic substrate,
The power module substrate, wherein the metal plate has a recess in a crystal grain boundary portion on its surface. The power module substrate according to claim 1, wherein the recess of the crystal grain boundary portion is a net shape along the crystal grain boundary portion in a plan view. The power module substrate according to claim 1 or 2, wherein the surface of the metal plate is provided with a metal film, and the metal film covers and adheres to an inner surface of the recess of the crystal grain boundary portion. The power module substrate according to claim 3, wherein the surface of the metal film is recessed in the upper part of the recess of the crystal grain boundary portion. The power module substrate according to claim 3 or 4, wherein the surface of the metal coating is a silver layer. A power module substrate according to any one of claims 1 to 5,
An electronic component mounted on the metal plate of the power module substrate.

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