SUBSTRATE FOR POWER MODULE AND METHOD OF PRODUCING SUBSTRATE FOR POWER MODULE

A substrate for a power module of the present disclosure includes: an insulation sheet; a plurality of front surface patterns formed on a front surface of the insulation sheet and disposed adjacent to each other with a gap between the plurality of front surface patterns in a direction in which the insulation sheet expands; a power semiconductor element connected to the front surface pattern; a plurality of rear surface patterns formed on a rear surface of the insulation sheet and disposed adjacent to each other with a gap between the plurality of rear surface patterns in the direction in which the insulation sheet expands; and a connection pattern disposed in the gap to fill the rear surface in the gap between the neighboring rear surface patterns of the plurality of rear surface patterns and configured to electrically connect the neighboring rear surface patterns, wherein each of the rear surface patterns and at least one front surface pattern overlap with the insulation sheet disposed therebetween in a direction perpendicular to the insulation sheet, and the plurality of rear surface patterns are formed so that thermal stress acting on the plurality of rear surface patterns and thermal stress acting on the plurality of front surface patterns are balanced.

CROSS-REFERENCE TO RELATED APPLICATION

Priority is claimed on Japanese Patent Application No. 2022-034300, filed Mar. 7, 2022, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

Background of the Invention

The present disclosure relates to a substrate for a power module and a method of producing a substrate for a power module.

Description of Related Art

For example, Japanese Unexamined Patent Application, First Publication No. 2013-157550 discloses a power module semiconductor device in which a second plate layer as a heat radiation sheet disposed on a rear surface of a ceramic substrate is divided by grooves and which is sealed with a resin by transfer molding. When a sealing resin is filled in the grooves formed in the second plate layer, the warping (deformation) of the entire module caused by a difference in thermal stress between the resin and the ceramic substrate is reduced.

SUMMARY OF THE INVENTION

Incidentally, when a current flowing through the first plate layer disposed on a surface changes (magnetic flux density change), a back electromotive force is generated in the second plate layer and an overcurrent flows therein. At this time, since the second plate layer is divided by the grooves, a path of the overcurrent flowing through the second plate layer is blocked. For this reason, a magnetic flux of the current flowing through the first plate layer and a magnetic flux of the overcurrent flowing through the second plate layer may not cancel each other out smoothly in some cases. As a result, parasitic inductance may increase in some cases.

The present disclosure is made to solve the above problems and an object of the present disclosure is to provide a substrate for a power module capable of reducing parasitic inductance while preventing deformation thereof caused by generation of thermal stress and a method of producing a substrate for a power module.

In order to achieve the above object, a substrate for a power module according to the present disclosure includes: an insulation sheet; a plurality of front surface patterns formed on a front surface of the insulation sheet and disposed adjacent to each other with a gap between the plurality of front surface patterns in a direction in which the insulation sheet expands; a power semiconductor element connected to the front surface pattern; a plurality of rear surface patterns formed on a rear surface of the insulation sheet and disposed adjacent to each other with a gap between the plurality of rear surface patterns in the direction in which the insulation sheet expands; and a connection pattern disposed in the gap to fill the rear surface in the gap between the neighboring rear surface patterns of the plurality of rear surface patterns and configured to electrically connect the neighboring rear surface patterns, in which each of the rear surface patterns and at least one front surface pattern of the plurality of front surface patterns overlap with the insulation sheet disposed therebetween in a direction perpendicular to the insulation sheet, and the plurality of rear surface patterns are formed so that thermal stress acting on the plurality of rear surface patterns and thermal stress acting on the plurality of front surface patterns are balanced.

A method of producing a substrate for a power module according to the present disclosure includes: a front surface pattern formation step of forming a plurality of front surface patterns disposed adjacent to each other with a gap between the plurality of front surface patterns in a direction in which an insulation sheet expands on a front surface of the insulation sheet; a rear surface pattern formation step of forming a plurality of rear surface patterns disposed adjacent to each other with a gap between the plurality of rear surface patterns in the direction in which the insulation sheet expands on a rear surface of the insulation sheet; a connection pattern formation step of forming a connection pattern disposed in the gap between the neighboring rear surface patterns of the plurality of rear surface patterns to fill the rear surface in the gap between the neighboring rear surface patterns and electrically connecting the neighboring rear surface patterns; and a power semiconductor element connection step of connecting a power semiconductor element to the front surface pattern, in which each of the rear surface patterns and at least one front surface pattern of the plurality of front surface patterns overlap with the insulation sheet disposed therebetween in a direction perpendicular to the insulation sheet, and the plurality of rear surface patterns are formed so that thermal stress acting on the plurality of rear surface patterns and thermal stress acting on the plurality of front surface patterns are balanced.

According to the present disclosure, it is possible to provide a substrate for a power module capable of reducing parasitic inductance while preventing deformation thereof caused by generation of thermal stress and a method of producing a substrate for a power module.

DETAILED DESCRIPTION OF THE INVENTION

A power conversion device according to an embodiment are described below with reference to the drawings.

A power conversion device is a device which converts direct current (DC) power into three-phase alternating current (AC) power or the like. Examples of the power conversion device in the embodiment include inverters used in systems such as power plants, inverters used for driving electric motors of electric vehicles or the like. In the embodiment, an inverter configured to control an electric motor (motor) is described as an example of the power conversion device.

As illustrated inFIG.1, a power conversion device100includes a casing1, an external input conductor2, a capacitor3, a power conversion part4, a connection conductor5, and a cooling device6.

The casing1forms an outer shell of the power conversion device100. The casing1in the embodiment is made of a metal such as aluminum, a synthetic resin, or the like and has a rectangular parallelepiped shape. The casing1has two lateral surfaces which are disposed back-to-back. Hereinafter, the two lateral surfaces are referred to as an input-side lateral surface1aand an output-side lateral surface1b. The external input conductor2configured to receive DC power as an input is drawn (protrudes) from the input-side lateral surface1a.

The external input conductor2is a pair of electrical conductors (bus bars) which supply DC power supplied from a DC power supply provided outside the power conversion device100to the capacitor3. The external input conductor2in the embodiment is formed of a metal including copper or the like. One end of the external input conductor2is connected to the capacitor3and the other end of the external input conductor2extends in a direction in which the other end crosses the input-side lateral surface1aof the casing1.

The capacitor3is a smoothing capacitor configured to store electric charge input from the external input conductor2and prevent voltage fluctuation caused by power conversion. The ripple-prevented and smoothed DC voltage is supplied to the power conversion part4through the capacitor3.

The power conversion part4converts a voltage input from the capacitor3. The power conversion part4in the embodiment includes three power modules40which are respectively responsible for outputs for a U phase, a V phase, and a W phase to output three-phase alternating current power. A constitution of the power modules40in the embodiment is described in detail later.

The connection conductor5is an electrical conductor (bus bar) configured to transmit electric power from the capacitor3to the power conversion part4. One end of the connection conductor5is connected to the capacitor3(detailed illustration of a connection state of the connection conductor5and the capacitor3is omitted). The other end of the connection conductor5is connected to the power module40.

The connection conductor5includes a first conductor51and a second conductor52. The first conductor51is a current path connecting a positive electrode (not shown) in the capacitor3and a positive electrode in the power module40. The second conductor52is a current path connecting a negative electrode (not shown) in the capacitor3and a negative electrode in the power module40. The first conductor51and the second conductor52are disposed side by side with an interval therebetween.

The cooling device6is a device which mainly cools the power modules40of the power conversion part4. The cooling device6is provided to be laminated on the casing and is fixed and integrated with the casing1. A liquid cooling medium such as water is introduced into the cooling device6from the outside. The liquid cooling medium is heated through heat-exchanging with the power modules40so that the power modules40are cooled.

The power modules40are devices in which input electric power is converted and output. The power modules40in the embodiment constitute a part of the power conversion part4. As illustrated inFIG.2, the power module40includes a base plate41, a substrate42for a power module, an outside output conductor43, and a reinforcing part44.

The base plate41is a member having a flat shape. The base plate41has a first surface41aand a second surface41bfacing a side opposite to that of the first surface41a. That is to say, the first surface41aand the second surface41bof the base plate41are disposed back-to-back in a state in which they are parallel each other.

The second surface41bof the base plate41is fixed to, for example, the cooling device6through a bonding material or the like (not shown). For example, copper is adopted for the base plate41in the embodiment. A metal such as aluminum may be adopted for the base plate41.

(Substrate for Power Module)

As illustrated inFIGS.3and4, the substrate42for a power module includes an insulation sheet420, front surface patterns421, power semiconductor elements422, rear surface patterns423, and a connection pattern424.

The insulation sheet420has a flat plate shape. The insulation sheet420has a front surface420aand a rear surface420bfacing a side opposite to that of the front surface420a. That is to say, the front surface420aand the rear surface420bof the insulation sheet420are disposed back-to-back in a state in which they are parallel each other.

The insulation sheet420in the embodiment is formed of, for example, an insulation material such as a ceramic. As the insulation material forming the insulation sheet420, instead of a ceramic, paper phenol, paper epoxy, a glass composite, glass epoxy, glass polyimide, a fluorine resin, or the like can be used.

The front surface patterns421are patterns of a copper foil or the like formed on the front surface420aof the insulation sheet420and expanding in a plane shape. The front surface patterns421are formed, for example, by being subjected to etching or the like after being fixed to the front surface420aof the insulation sheet420using adhesion or the like. A thickness of the front surface pattern421in the embodiment is set to 200 to 800 μm.

The plurality of front surface patterns421are disposed on the front surface420aof the insulation sheet420. The plurality of front surface patterns421are disposed adjacent to each other with a gap R therebetween in a direction in which the insulation sheet420expands. In the embodiment, a case in which the three front surface patterns421are disposed on the front surface420ais described as an example. These three front surface patterns421are formed to have the same thickness.

For convenience of explanation, hereinafter these three front surface patterns421are referred to as a first front surface pattern421a, a second front surface pattern421b, and a third front surface pattern421c.

The first conductor51as a positive electrode configured to receive a DC current as an input is connected to the first front surface pattern421a. The second conductor52as a negative electrode configured to output a DC current is connected to the second front surface pattern421b. The outside output conductor43configured to output an AC current obtaining through conversion using the power semiconductor elements422to a load such as a motor or the like (not shown) provided outside the power conversion device100is connected to the third front surface pattern421c.

The power semiconductor elements422are circuit elements in which electric power is converted through a switching operation in which a voltage and a current is turned on and off. The power semiconductor elements422are, for example, switching elements such as an insulated gate bipolar transistor (IGBT) and a metal-oxide-semiconductor field effect transistor (MOSFET). In the embodiment, the six power semiconductor elements422are connected to the front surface patterns421of the substrate42for a power module.

The six power semiconductor elements422in the embodiment are composed of three first power semiconductor elements422aand three second power semiconductor elements422b. The first power semiconductor elements422aare connected to the first front surface pattern421a. The second power semiconductor elements422bare connected to the third front surface pattern421c.

When the power semiconductor elements422are IGBTs, each of the power semiconductor elements422has an input surface on which an input terminal corresponding to a collector is formed, an output surface on which an output terminal corresponding to an emitter is formed, and a gate corresponding to a control signal input terminal configured to control switching of the power semiconductor element422.

An input surface of the power semiconductor element422is electrically connected to the front surface patterns421through a bonding material S or the like. For example, one end of a bonding wire (not shown) as a conducting wire is electrically connected to the output surface of the power semiconductor element422.

An input surface of the first power semiconductor element422ais connected to the first front surface pattern421a. The other end of the bonding wire connected to an output surface of the first power semiconductor element422ais connected to the third front surface pattern421c. An input surface of each of the second power semiconductor elements422bis connected to the third front surface pattern421c. The other end of the bonding wire connected to an output surface of the second power semiconductor element422bis connected to the second front surface pattern421b.

DC power is input to an input terminal of each of the first power semiconductor elements422athrough the first front surface pattern421aand the input DC power is converted into AC power by the first power semiconductor element422a. The converted AC power is output from an output terminal (not shown) in the first power semiconductor element422ato the third front surface pattern421cthrough the bonding wire.

AC power is input to an input terminal in the second power semiconductor element422bthrough the third front surface pattern421cand the input AC power is converted into DC power by the second power semiconductor element422b. The converted DC power is output from an output terminal (not shown) in the second power semiconductor element422bto the second front surface pattern421bthrough the bonding wire.

A control signal generated by a control part (not shown) provided outside the substrate42for a power module is input to the power semiconductor element422. The power semiconductor element422performs switching in accordance with the control signal. When the power semiconductor elements422are MOSFETs, each of the power semiconductor elements422includes an input surface corresponding to a drain, an output surface corresponding to a source, and a gate corresponding to a control signal input terminal.

The rear surface patterns423are patterns of a copper foil or the like formed on the rear surface420bof the insulation sheet420and expanding in a plane shape. The rear surface patterns423are formed, for example, by being subjected to etching or the like after being fixed to the rear surface420bof the insulation sheet420using adhesion or the like. The plurality of rear surface patterns423are disposed on the rear surface420bof the insulation sheet420. A thickness of each of the rear surface patterns423in the embodiment is the same as a thickness of each of the front surface patterns421.

The plurality of rear surface patterns423are disposed adjacent to each other with a gap R in a direction in which the insulation sheet420expands. In the embodiment, a case in which the three rear surface patterns423are disposed on the front surface420ais described as an example. For convenience of explanation, hereinafter these three rear surface patterns423are referred to as a first rear surface pattern423a, a second rear surface pattern423b, and a third rear surface pattern423c.

The first rear surface pattern423ain the embodiment faces the first front surface pattern421awith the insulation sheet420disposed therebetween in a direction perpendicular to the insulation sheet420. The first rear surface pattern423aand the first front surface pattern421ahave the same shape. The “same shape” as described herein refers to substantially the same shape and slight production errors and design tolerances therein are allowed.

The second rear surface pattern423bin the embodiment faces the second front surface pattern421bwith the insulation sheet420disposed therebetween in the direction perpendicular to the insulation sheet420. The second rear surface pattern423band the second front surface pattern421bhave the same shape. The third rear surface pattern423cin the embodiment faces the third front surface pattern421cwith the insulation sheet420disposed therebetween in the direction perpendicular to the insulation sheet420. The third rear surface pattern423cand the third front surface pattern421chave the same shape.

Therefore, the front surface pattern421and the rear surface pattern423facing each other with the insulation sheet420disposed therebetween in the direction perpendicular to the insulation sheet420have the same shape. That is to say, the plurality of rear surface patterns423are formed so that the thermal stress acting on the plurality of rear surface patterns423and the thermal stress acting on the plurality of front surface patterns421are balanced.

The term “balance” of thermal stress described herein means that, when heat is distributed over the entire substrate42for a power module due to a current flowing through the front surface patterns421or heat generation due to switching of the power semiconductor element422as a heat source, magnitudes of the thermal stresses acting on the front surface pattern421and the rear surface pattern423are substantially the same. Therefore, it is considered that the thermal stresses are balanced in a state in which a difference in thermal stress caused by a temperature difference between the front surface pattern421and the rear surface pattern423due to a position of the heat source or the like is allowed.

The rear surface pattern423is fixed to a center of the first surface41aof the base plate41through the bonding material S or the like. For example, solder, a sintered material (powder of a metal or the like), or the like can be adopted for the bonding material S used for bonding the base plate41and the rear surface pattern423, bonding the power semiconductor element422and the front surface pattern421, and bonding the base plate41and the cooling device6.

The connection pattern424is a pattern of a copper foil or the like disposed with the gap R to fill the rear surface420bin the gap R between the neighboring rear surface patterns423. The connection pattern424electrically connects the neighboring rear surface patterns423.

The rear surface pattern423is formed, for example, by being subjected to etching or the like after being fixed to the rear surface420bof the insulation sheet420using adhesion or the like. A thickness of the connection pattern424is thinner than thicknesses of the front surface pattern421and the rear surface pattern423. The thickness of the connection pattern424in the embodiment is assumed to be 50 μm or less.

As illustrated inFIGS.2and3, the outside output conductor43is an electrical conductor (bus bar) configured to output the AC power which are converted by the power semiconductor element422to the outside of the power conversion device100. One end of the outside output conductor43is connected to the third front surface pattern421cin the substrate42for a power module.

Here, as illustrated inFIG.1, the other end of the outside output conductor43extends further outward than the output-side lateral surface1bof the casing1. The other end of the outside output conductor43is connected to a current output wiring (not shown) connected to a load such as a motor.

The reinforcing part44is a member which is fixed to the first surface41aof the base plate41and mechanically reinforces the connection conductor5and the outside output conductor43. The reinforcing part44is formed of a synthetic resin material or the like. The reinforcing part44covers a part of the connection portion and the outside output conductor43from the outside thereof and surrounds the substrate42for a power module from the outside thereof. That is to say, as illustrated inFIG.2, the reinforcing part44forms a case which surrounds the substrate42for a power module in a direction along the substrate42for a power module (surrounds the substrate42for a power module along the circumference of the substrate42for a power module).

The reinforcing part44is fixed to the first surface41aof the base plate41through an adhesive or the like. For the reinforcing part44in the embodiment, for example, an insulation material such as polyphenylene sulfide (PPS) can be adopted as a synthetic resin material. Insulation materials other than PPS may be adopted for the reinforcing part44.

The reinforcing part44defines a space together with the substrate42for a power module. In the embodiment, hereinafter the space defined by the reinforcing part44and the substrate42for a power module is referred to as a potting space P. A liquid potting material is poured (potted) into the potting space P from the outside and the front surface pattern421and the power semiconductor element422of the insulation sheet420exposed in the potting space P are sealed.

A potting material poured into the potting space P is cured after a certain amount of time, and then, the front surface patterns421and the power semiconductor element422of the substrate42for a power module are electrically insulated from the space outside the power module40. For example, silicone gel or an epoxy resin is adopted for the potting material in the embodiment. Synthetic resins other than the silicone gel or the epoxy resin may be used as the potting material.

(Method of Producing Substrate for Power Module)

A method of producing the substrate42for a power module in the embodiment is described below with reference toFIG.5. The production method includes a front surface pattern formation step S1, a rear surface pattern formation step S2, a connection pattern formation step S3, and a power semiconductor element connection step S4.

The front surface pattern formation step S1is a step of forming the plurality of front surface patterns421on the front surface420aof the insulation sheet420. In the front surface pattern formation step S1, after a metal pattern of a copper foil or the like is fixed to the rear surface420bof the insulation sheet420using adhesion or the like, processing such as etching is performed. Thus, the front surface patterns421are formed on the front surface420aof the insulation sheet420.

The rear surface pattern formation step S2is a step performed after the front surface pattern formation step S1. In the rear surface pattern formation step S2, the plurality of rear surface patterns423are formed on the rear surface420bof the insulation sheet420. In the rear surface pattern formation step S2, after a metal pattern of a copper foil or the like is fixed to the rear surface420bof the insulation sheet420using adhesion or the like, processing such as etching is performed. Thus, the rear surface patterns423are formed on the rear surface420bof the insulation sheet420.

The connection pattern formation step S3is a step performed after the rear surface pattern formation step S2. In the connection pattern formation step S3, the connection pattern424filling the rear surface420bof the insulation sheet420in the gap R between the neighboring rear surface patterns423is formed. That is, in the connection pattern formation step S3, the connection pattern424filling the gap R between the neighboring rear surface patterns423is formed on the rear surface420bof the insulation sheet420.

In the connection pattern formation step S3, after a metal pattern of a copper foil or the like is fixed to the rear surface420bof the insulation sheet420in the gap R between the neighboring rear surface patterns423using adhesion or the like, processing such as etching is performed. Thus, the connection pattern424is formed on the rear surface420bof the insulation sheet420and the neighboring rear surface patterns423are electrically connected.

The power semiconductor element connection step S4is a step performed after the connection pattern formation step S3. In the power semiconductor element connection step S4, the power semiconductor elements422are connected to the front surface patterns421. In the power semiconductor element connection step S4, the bonding material S is applied to predetermined installation places on the front surface patterns421.

Subsequently, the power semiconductor elements422are installed on the front surface pattern421so that the input surface of the power semiconductor element422is in contact with the bonding material S applied to the installation place of the front surface pattern421. Furthermore, these parts are loaded inside a furnace heated to a predetermined temperature for a predetermined period of time. That is, the insulation sheet420, on which the plurality of front surface patterns421, the rear surface patterns423and the connection pattern424are formed, the bonding material S is applied and the power semiconductor elements422are installed, are loaded inside a furnace heated to a predetermined temperature for a predetermined period of time. Thus, the bonding material S between the input surface of the power semiconductor element422and the front surface pattern421is melted to complete soldering (installation of the power semiconductor elements422).

Through the above series of steps, the substrate42for a power module is produced.

After a current input to the front surface pattern421through the first conductor51as a positive electrode is converted by the first power semiconductor element422a, the converted current is used to rotate a motor or the like provided outside the power conversion device100through the outside output conductor43. After the current used for the rotation of the motor or the like flows to the front surface pattern421again through the outside output conductor43and is converted by the second power semiconductor element422b, the converted current returns to the capacitor3through the second conductor52as a negative electrode. When a voltage input to the front surface pattern421is converted by the power semiconductor element422, heat is generated.

Also, since a magnitude of a current flowing in the front surface pattern421changes rapidly due to the switching of the power semiconductor element422, a magnetic flux density of the current flowing in the front surface pattern421changes rapidly in accordance with the change of the magnitude of the current flowing in the front surface pattern421. At this time, a back electromotive force (overcurrent) which generates a magnetic flux in which the change in magnetic flux density is cancelled out is generated in the rear surface pattern423formed on the rear surface420bof the insulation sheet420.

According to the above constitution, since a difference is not generated between the thermal stress acting on the front surface pattern421and the thermal stress acting on the rear surface pattern423, the front surface pattern421and the rear surface pattern423thermally expand in the same way. Furthermore, since a thickness of the connection pattern424is thinner than a thickness of each of the rear surface pattern423, it is possible to prevent the occurrence of a difference in thermal stress between the front surface420aside and the rear surface420bside, compared to the constitution in which the rear surface pattern423that is a single metal pattern having a uniform thickness is formed (the constitution in which, on the rear surface420bof the insulation sheet420, only one rear surface pattern423that is a metal pattern having a uniform thickness is formed and no connection pattern424is formed) is provided. Therefore, it is possible to prevent damage of the substrate42for a power module.

Also, an overcurrent, which is generated in the rear surface pattern423in accordance with the change in the magnetic flux density of the current flowing through the front surface pattern421, flows through each of the rear surface patterns423through the connection pattern424. That is to say, a path of the overcurrent flowing through the rear surface pattern423is not blocked, compared to the constitution in which the rear surface patterns423are not electrically connected.

Therefore, it is possible to effectively reduce parasitic inductance while preventing the deformation of the entire substrate42for a power module. That is to say, it is possible to prevent damage of the substrate42for a power module and improve the power conversion efficiency of the substrate42for a power module.

OTHER EMBODIMENTS

Although the embodiment of the present disclosure is described in detail above with reference to the drawings, the specific constitution is not limited to the constitution of the embodiment, and additions, omissions, substitutions and other modifications of the constitution may be provided without departing from the scope of the present disclosure.

Although a constitution in which the front surface pattern421and the rear surface pattern423facing each other with the insulation sheet420disposed therebetween in the direction perpendicular to the insulation sheet420have the same shape is described in the embodiment, the present disclosure is not limited to this constitution. That is to say, the shape of the front surface patterns421and the shape of the rear surface patterns423may be different from each other. In this case, each of the rear surface patterns423and at least one front surface pattern421of the plurality of front surface patterns421may overlap with the insulation sheet420disposed therebetween and the plurality of rear surface patterns423and the plurality of front surface patterns421may be formed so that the thermal stress acting on the plurality of rear surface patterns423and the thermal stress acting on the plurality of front surface patterns421are balanced.

Also, although the constitution in which the number of rear surface patterns423formed on the rear surface420bof the insulation sheet420is the same as the number of front surface patterns421formed on the front surface420aof the insulation sheet420and the thickness of the rear surface patterns423is the same as the thickness of the front surface patterns421is described in the embodiment, the present disclosure is not limited to this constitution. For example, a constitution in which the number of rear surface patterns423is greater than the number of front surface patterns421and the thickness of the rear surface pattern423is thinner than the thickness of the front surface pattern421may be provided. Furthermore, for example, a constitution in which the number of rear surface patterns423is less than the number of front surface patterns421and the thickness of the rear surface pattern423is greater than the thickness of the front surface pattern421may be provided. In these cases, each of the rear surface patterns423and at least one front surface pattern421of the plurality of front surface patterns421may overlap with the insulation sheet420disposed therebetween and the plurality of rear surface patterns423and the plurality of front surface patterns421may be formed so that the thermal stress acting on the plurality of rear surface patterns423and the thermal stress acting on the plurality of front surface patterns421are balanced.

Furthermore, although the constitution in which the thickness of the connection pattern424is 50 μm or less is described in the embodiment, the thickness of the connection pattern424of the present disclosure is not limited to this numerical value. The thickness of the connection pattern424may be, for example, one-fifth or less of the thickness of the rear surface patterns423(the front surface patterns421).

In addition, although a constitution in which the thickness of the connection pattern424is thinner than the thicknesses of the front surface patterns421and the rear surface patterns423is described in the embodiment, the present disclosure is not limited to this constitution. For example, if the connection pattern424electrically connects the rear surface patterns423so that the thermal stress acting on the front surface patterns421and the thermal stress acting on the rear surface patterns423are balanced and so that the thermal expansion of the rear surface patterns423is not prevented, the thickness of the connection pattern424may be greater than or equal to the thickness of the rear surface patterns423.

Moreover, although the constitution in which the connection pattern424is the metal pattern disposed in the gap R to fill the rear surface420bin the gap R between the neighboring rear surface patterns423is described in the embodiment, the present disclosure is not limited to this constitution. For example, the constitution in which the plurality of connection patterns424are disposed at intervals so that each of the connection patterns424serves as a bridge between the rear surface patterns423in the gap R between the rear surface patterns423and the connection pattern424electrically connects the neighboring rear surface patterns423may be provided.

Also, although the constitution in which each of the front surface patterns421, the rear surface patterns423, and the connection pattern424is a copper pattern is described in the embodiment, the present disclosure is not limited to this constitution. The front surface patterns421, the rear surface patterns423, or the connection pattern424may be formed of aluminum, an alloy, or the like. In this case, the metal pattern used in the front surface pattern formation step S1, the rear surface pattern formation step S2, or the connection pattern formation step S3in the method of producing the substrate42for a power module is formed of aluminum, an alloy, or the like. Furthermore, the connection pattern424may be formed of solder or the like.

In addition, the front surface patterns421may be formed of copper and the rear surface patterns423may be formed of aluminum. Furthermore, the front surface patterns421may be formed of aluminum and the rear surface patterns423may be formed of copper. Therefore, the front surface patterns421and the rear surface patterns423may be formed of different metal materials.

Also, although the constitution in which the first surface41aand the second surface41bof the base plate41and the front surface420aand the rear surface420bof the insulation sheet420have a relationship in which they are disposed back-to-back in a state in which they are parallel each other is described in the embodiment, the present disclosure is not limited to this constitution and they may be slightly inclined to each other.

Also, although the inverter is described as an example of the power conversion device100in the embodiment, the power conversion device100of the present disclosure is not limited to the inverter. The power conversion device100may be, for example, a device which converts electric power using the power semiconductor elements422such as a converter and a device obtained by combining an inverter and a converter. When the power conversion device100is a converter, the power conversion device100may have a constitution in which an AC voltage is input from an external input power supply (not shown) to the outside output conductor43, the power semiconductor elements422converts the AC voltage into a DC voltage, and the DC voltage from the power semiconductor elements422is output from an input part (the connection conductor5).

Furthermore, although the connection pattern formation step S3is performed after the rear surface pattern formation step S2in the method of producing the substrate42for a power module described in the embodiment, the present disclosure is not limited thereto. The connection pattern formation step S3may be omitted and the rear surface patterns423and the connection pattern424may be integrally formed on the rear surface420bof the insulation sheet420from the beginning, for example, using a lamination shaping device such as a metal3D printer in the rear surface pattern formation step S2.

In addition, the rear surface pattern formation step S2is performed after the front surface pattern formation step S1in the method of producing the substrate42for a power module described in the embodiment, the present disclosure is not limited thereto. The front surface pattern formation step S1may be performed after the connection pattern formation step S3. In this case, the power semiconductor element connection step S3is performed after the front surface pattern formation step S1.

The substrate for a power module and the method of producing the substrate for a power module described in the embodiment are ascertained, for example, as follows.

(1) A substrate42for a power module according to a first aspect includes: an insulation sheet420; a plurality of front surface patterns421formed on a front surface420aof the insulation sheet420and disposed adjacent to each other with a gap R between the plurality of front surface patterns421in a direction in which the insulation sheet420expands; a power semiconductor element422connected to the front surface pattern421; a plurality of rear surface patterns423formed on a rear surface420bof the insulation sheet420and disposed adjacent to each other with a gap R between the plurality of rear surface patterns423in the direction in which the insulation sheet420expands; and a connection pattern424disposed in the gap R to fill the rear surface420bin the gap R between the neighboring rear surface patterns423of the plurality of rear surface patterns423and configured to electrically connect the neighboring rear surface patterns423, in which each of the rear surface patterns423and at least one front surface pattern421of the plurality of front surface patterns421overlap with the insulation sheet420disposed therebetween in a direction perpendicular to the insulation sheet420, and the plurality of rear surface patterns423are formed so that thermal stress acting on the plurality of rear surface patterns423and thermal stress acting on the plurality of front surface patterns421are balanced.

Thus, the front surface patterns421and the rear surface patterns423thermally expand in the same way. Furthermore, since a thickness of the connection pattern424is thinner than a thickness of the rear surface pattern423, it is possible to prevent the occurrence of a difference in thermal stress between the front surface420aside and the rear surface420bside, compared to the constitution in which the rear surface pattern423that is a single metal pattern is formed (the constitution in which, on the rear surface420bof the insulation sheet420, only one rear surface pattern423that is a metal pattern is formed). In addition, since the connection pattern424electrically connects the neighboring rear surface patterns423, a path of an overcurrent flowing through the rear surface patterns423is not blocked.

(2) A substrate42for a power module according to a second aspect is the substrate42for a power module in (1), in which a thickness of the connection pattern424may be thinner than a thickness of each of the plurality of the rear surface patterns423.

Thus, it is possible to realize the above actions by a more specific constitution. Furthermore, it is possible to further prevent deformation of the substrate42for a power module.

(3) A substrate42for a power module according to a third aspect is the substrate42for a power module in (1) or (2), in which the number of the rear surface patterns423may be the same as the number of the front surface patterns421.

Thus, it is possible to realize the above actions by a more specific constitution. Furthermore, it is possible to further prevent deformation of the substrate42for a power module.

(4) A substrate42for a power module according to a fourth aspect is the substrate42for a power module in any one of (1) to (3), in which the front surface pattern421and the rear surface pattern423facing each other with the insulation sheet420disposed therebetween in a direction perpendicular to the insulation sheet420may have the same shape.

Thus, it is possible to realize the above actions by a more specific constitution. Furthermore, it is possible to further prevent deformation of the substrate42for a power module.

(5) A method of producing a substrate42for a power module according to a fifth aspect includes: a front surface pattern formation step S1of forming a plurality of front surface patterns421disposed adjacent to each other with a gap R between the plurality of front surface patterns421in a direction in which an insulation sheet420expands on a front surface420aof the insulation sheet420; a rear surface pattern formation step S2of forming a plurality of rear surface patterns423disposed adjacent to each other with a gap R between the plurality of rear surface patterns423in the direction in which the insulation sheet420expands on a rear surface420bof the insulation sheet420; a connection pattern formation step S3of forming a connection pattern424disposed in the gap R between the neighboring rear surface patterns of the plurality of rear surface patterns to fill the rear surface420bin the gap R between the neighboring rear surface patterns423and electrically connecting the neighboring rear surface patterns423; and a power semiconductor element connection step S4of connecting a power semiconductor element422to the front surface pattern421, in which each of the rear surface patterns423and at least one front surface pattern421of the plurality of front surface patterns421overlap with the insulation sheet420disposed therebetween in a direction perpendicular to the insulation sheet420, and the plurality of rear surface patterns423are formed so that thermal stress acting on the plurality of rear surface patterns423and thermal stress acting on the plurality of front surface patterns421are balanced.

Thus, it is possible to produce the substrate42for a power module capable of reducing parasitic inductance while preventing the deformation thereof caused by the generation of thermal stress.

According to the present disclosure, it is possible to provide the substrate42for a power module capable of reducing parasitic inductance while preventing deformation thereof caused by generation of thermal stress and the method of producing the substrate42for a power module.

EXPLANATION OF REFERENCES