Power module

A power module includes a power semiconductor element, an interconnection material, a circuit board, an external terminal, a joining material, and a sealing resin. A clearance portion is continuously formed between the sealing resin and each of an end surface of the joining material and a surface of the interconnection material so as to extend from the end surface of the joining material to the surface of the interconnection material, the end surface of the joining material being located between the power semiconductor element and the interconnection material, the surface of the interconnection material being located between the end surface and a predetermined position of the interconnection material separated by a distance from the end surface.

TECHNICAL FIELD

The present invention relates to a power module, particularly, a power module in which a power semiconductor element is sealed with a resin.

BACKGROUND ART

A power module for controlling power includes a power semiconductor element such as a diode, an insulated gate bipolar transistor (IGBT), or a metal oxide semiconductor field effect transistor (MOSFET).

In each of these power semiconductor elements, respective electrodes are formed on two surfaces thereof facing each other. A circuit board or interconnection material is electrically connected to each of the electrodes and the power semiconductor element is insulatively sealed with a sealing resin, thus manufacturing the power module.

The power semiconductor element is electrically connected to the circuit board by joining the power semiconductor element onto the circuit board with a joining material, such as a solder, being interposed therebetween, for example. Moreover, for example, in the case of a power module for large current, the power semiconductor element is electrically connected to the interconnection material by joining a plate-like interconnection material onto each of the electrodes of the power semiconductor element with the joining material, such as a solder, being interposed therebetween.

The plate-like interconnection material has a linear expansion coefficient greatly different from that of the power semiconductor element. For example, copper, which is frequently used as such a plate-like interconnection material, has a linear expansion coefficient of about 17 ppm/° C. (17 μm/° C./m). On the other hand, silicon, which is frequently used as such a power semiconductor element, has a linear expansion coefficient of about 3 ppm/° C. (3 μm/° C./m). When a temperature (environmental temperature) around the semiconductor module or a temperature of the power semiconductor element itself is fluctuated, the difference in linear expansion coefficient therebetween leads to application of thermal stress to the joining material for connecting the plate-like interconnection material to the power semiconductor element. Repeated application of thermal stress to the joining material causes a generation of a crack in the joining material, thus resulting in a deteriorated function of the power module, disadvantageously.

In order to overcome such a problem, the following method is employed: a curable sealing resin is used as an insulation sealing for the power module to mechanically bind the power semiconductor element, the joining material, and the plate-like interconnection material, thereby reinforcing the joining material. The insulation sealing by the sealing resin is performed by: surrounding, with an uncured insulation resin, the power semiconductor element connected to the circuit board, the interconnection material, and the like; and curing the resin in that state.

As one example thereof, there is the following method: a power semiconductor element connected to a circuit board, an interconnection material, and the like is set in a metal mold, then an uncured sealing resin is poured into the metal mold, and the sealing resin is cured under application of pressure. As another example, there is the following method: a circuit board to which a power semiconductor element is joined is joined to a base plate; a case having a shape surrounding the circumference of the power semiconductor element is adhered onto the base plate; and then an uncured sealing resin is poured into the case and is cured.

However, generally, since the linear expansion coefficient of the sealing resin is larger than the linear expansion coefficient of the power semiconductor element, shear stress is generated at an interface between the sealing resin and the power semiconductor element when an environmental temperature or temperature of the power semiconductor element itself is fluctuated. When adhesion force of the sealing resin to the power semiconductor element is weak, the sealing resin may be detached from the power semiconductor element, thus resulting in a decreased insulating property between the electrodes of the power semiconductor element, disadvantageously.

For example, as a method for preventing such detachment of the sealing resin from the power semiconductor element, each of Patent Document 1 and Patent Document 2 proposes the following method: a polyimide film having strong adhesion force to a sealing resin is formed on a power semiconductor element connected to a circuit board, an interconnection material, and the like, and they are sealed with a sealing resin from above the polyimide film.

Furthermore, Patent Document 2 proposes a method for detaching the sealing resin from a portion of the surface of the interconnection material at a position distant from each of the power semiconductor element and the joining material. In this method, the sealing resin at the position distant away from the joining material is detached to relax stress, thereby suppressing detachment of the sealing resin from the surface of the joining material and the surface of the power semiconductor element.

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

Still in the case of the conventional power module, the sealing with the resin needs to be performed after forming a certain film such as the polyimide film on the power semiconductor element connected to the circuit board, the interconnection material, and the like. However, since the power semiconductor element connected to the circuit board, the interconnection material, and the like has a complicated shape, it is difficult to form a uniform film. Therefore, a relatively complicated process is required.

The present invention has been made to solve the foregoing problem, and has an object to provide a power module that can prevent the sealing resin from being detached from a power semiconductor element or the like, in a simple manner.

Solution to Problem

A power module according to the present invention includes a power semiconductor element, an interconnection material, a joining material, a circuit board, and a sealing resin. The power semiconductor element has a first surface and a second surface facing each other, a first electrode is formed on the first surface, and a second electrode is formed on the second surface. The interconnection material is disposed to face the first surface of the power semiconductor element. The joining material is formed between the first electrode and the interconnection material to electrically and mechanically connect the first electrode to the interconnection material. The circuit board is disposed to face the second surface of the power semiconductor element and is electrically and mechanically connected to the second electrode. The sealing resin seals the power semiconductor element, the interconnection material, the joining material, and the circuit board. A clearance portion is provided between the sealing resin and each of an end surface of the joining material and a surface of the interconnection material so as to extend from the end surface of the joining material to the surface of the interconnection material, the end surface of the joining material being located between the power semiconductor element and the interconnection material, the surface of the interconnection material being located between the end surface and a position of the interconnection material separated by a distance from the end surface.

Advantageous Effects of Invention

According to the power module according to the present invention, the clearance portion is formed between the sealing resin and each of the end surface of the joining material and the surface of the interconnection material so as to extend from the end surface of the joining material to the surface of the interconnection material, the end surface of the joining material being located between the power semiconductor element and the interconnection material, the surface of the interconnection material being located between the end surface and the position of the interconnection material separated by a distance from the end surface. Accordingly, stress is relaxed at the interface between the power semiconductor element and the sealing resin, with the result that the sealing resin is less likely to be detached from the power semiconductor element. Accordingly, detachment of the sealing resin can be suppressed from being developed.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Here, the following describes a power module in which a plate-like interconnection material is applied as an interconnection material electrically connected to a power semiconductor element.

As shown inFIG. 1, a power module PM includes a power semiconductor element4, an interconnection material2, a circuit board6, an external terminal8, joining materials5,7, and a sealing resin1. Power semiconductor element4has two surfaces facing each other, and respective electrodes (not shown) are formed on one surface and the other surface of power semiconductor element4. Interconnection material2is in the form of a flat plate. Circuit board6includes: an insulating substrate602having two surfaces facing each other; and metal plates601,603. Metal plate601is disposed on one surface of insulating substrate602, and metal plate603is disposed on the other surface of insulating substrate602.

Interconnection material2in the form of a flat plate is electrically and mechanically connected, through joining material5, to the electrode formed on one surface of power semiconductor element4. Metal plate601of circuit board6is electrically and mechanically connected, through joining material7, to the electrode formed on the other surface of power semiconductor element4. Moreover, external terminal8is electrically and mechanically connected to metal plate601through a joining material (not shown), an ultrasonic joining method, or the like.

Insulating substrate602is composed of: a ceramic such as aluminum oxide, aluminum nitride, or silicon nitride; or an insulator such as an epoxy resin, for example. Each of metal plates601,603is composed of a conductor such as copper or aluminum. As each of joining materials5,7, a solder or the like is applied, for example.

Sealing resin1insulatively seals power semiconductor element4, circuit board6, joining materials5,7, and external terminal8such that respective portions (end portions) of interconnection material2and external terminal8project from sealing resin1and the surface of metal plate603of circuit board6is exposed. Sealing resin1is thermally curable, such as an epoxy resin. The respective portions of interconnection material2and external terminal8projecting from sealing resin1are used as input/output terminals for current and voltage. Moreover, the exposed surface (bottom surface) of metal plate603is used as a surface to be connected to a heat sink.

In this power module PM, clearance portions3are provided by detaching sealing resin1from interconnection material2and joining material5. Each of clearance portions3is formed between sealing resin1and each of an end surface of joining material5and a surface of interconnection material2so as to extend from the end surface of joining material5to the surface of interconnection material2, the end surface of joining material5being located between power semiconductor element4and interconnection material2, the surface of interconnection material2being located between the end surface and a position of interconnection material2separated by a distance from the end surface. A small clearance is formed in clearance portion3. It should be noted that inFIG. 1and the like, for the ease of description, the clearance is illustrated in an exaggerated manner.

Here, in this specification, clearance portion3refers to a space formed between sealing resin1and the end surface of joining material5, or refers to a space formed between sealing resin1and the surface of interconnection material2. Clearance portion3is a region surrounded by sealing resin1, joining material5, interconnection material2, and power semiconductor element4. Moreover, the expression “clearance” is not intended to define whether the space is formed artificially or spontaneously.

In order to provide clearance portion3, a material having relatively weak adhesion force to sealing resin1is selected as joining material5, and a solder is applied thereto, for example. Moreover, interconnection material2has a partial surface201at which clearance portion3is to be located and which has been previously through a process for decreasing the adhesion force to the sealing resin.

This will be described more in detail as follows. Joining material5is selected such that the adhesion force between joining material5and sealing resin1becomes the weakest among the adhesion force between interconnection material2and sealing resin1, the adhesion force between power semiconductor element4and sealing resin1, the adhesion force between metal plate601and sealing resin1, and the adhesion force between joining material5and sealing resin1. Examples of such a joining material5include a lead-free solder including Sn. Specific examples thereof include a material such as a Sn—Cu alloy, a Sn—Ag alloy or a Sn—Ag—Cu alloy. Each of the above-described adhesion forces can be measured in advance by a pudding cup test or the like, for example. It should be noted that the pudding cup test refers to a method for performing a shearing strength test with a pudding-cup shaped resin being formed on a surface of an appropriate member.

Mounting steps of power module PM are performed in the following order: a step of joining power semiconductor element4to circuit board6; a step of joining interconnection material2to power semiconductor element4; and a step of performing insulation sealing with sealing resin1. External terminal8may be joined to circuit board6in any time as long as external terminal8is joined to circuit board6before the insulation sealing. Here, during the insulation sealing with thermally curable sealing resin1, the whole of power module PM is exposed to a temperature environment of about 100 to 200° C. in order to cure sealing resin1. When the temperature is reduced to the room temperature after sealing resin1is cured, a thermal stress is caused at an interface between sealing resin1and the structure due to the difference in the linear thermal expansion coefficient therebetween.

On this occasion, since the material having relatively weak adhesion force to sealing resin1is selected as joining material5, sealing resin1is preferentially detached from the interface between joining material5and sealing resin1due to the thermal stress when the temperature is reduced to the room temperature.

Partial surface201of interconnection material2at which clearance portion3is to be located is a position adjacent to joining material5or a position close to joining material5. Moreover, surface201of interconnection material2is located at the surface thereof facing power semiconductor element4. The area of surface201is smaller than the total area of the interface between surface A of interconnection material2and sealing resin1.

Surface201of interconnection material2has been previously through the process for decreasing the adhesion force to sealing resin1. Accordingly, when the temperature is reduced to the room temperature after curing sealing resin1, sealing resin1is detached from surface201due to the thermal stress. Here, examples of the process for decreasing the adhesion force between surface201of interconnection material2and sealing resin1include: a method for applying nickel (Ni) plating to interconnection material2; a method for adhering a lead-free solder to the surface of interconnection material2; and a method for smoothing the surface of interconnection material2. Each of the methods above may be performed in any time in the mounting steps as long as it is performed before the insulation sealing.

The Ni plating and the lead-free solder can be formed on the surface of interconnection material2through pattern plating or the like. Moreover, when the lead-free solder is used for joining material5, an amount of supply of the lead-free solder is increased to wet surface201, thereby forming the lead-free solder on the surface of interconnection material2. The surface can be made smooth in accordance with any polishing method.

In addition to these, there is a method for applying a parting agent to the surface of interconnection material2. In this method, the parting agent is applied to the surface of interconnection material2, thereby decreasing the adhesion force between surface201of interconnection material2and sealing resin1. This method is desirably performed in the mounting steps by, for example, joining interconnection material2to power semiconductor element4and then applying a droplet thereof via a tip of a needle before insulatively sealing with sealing resin1.

By performing such a process, clearance portion3is continuously formed between sealing resin1and each of the end surface of joining material5and the surface of interconnection material2so as to extend from the end surface of joining material5to the surface of interconnection material2, the end surface of joining material5being located between power semiconductor element4and interconnection material2, the surface of interconnection material2being located between the end surface and a position of interconnection material2separated by a distance from the end surface.

In power module PM, clearance portion3is continuously formed between sealing resin1and each of the end surface of joining material5and the surface of interconnection material2so as to extend from the end surface of joining material5to the surface of interconnection material2, the surface of interconnection material2being located between the end surface and a position of interconnection material2separated by a distance from the end surface. Accordingly, stress is relaxed at the interface between power semiconductor element4and sealing resin1, with the result that sealing resin1is less likely to be detached from power semiconductor element4. Accordingly, detachment of sealing resin1can be suppressed from being developed.

Particularly, since clearance portion3is provided to include the end surface of joining material5at a portion at which power semiconductor element4and interconnection material2are closest to each other, it is possible to effectively relax the stress resulting from the difference in linear expansion coefficient between power semiconductor element4and interconnection material2, as compared with a case where clearance portion3is provided at a position distant away from the power semiconductor element and the joining material.

Furthermore, in order to effectively prevent development of detachment, a position to which detachment of sealing resin1is supposed to be developed is subjected to a process for increasing adhesion force between sealing resin1and interconnection material2. As shown inFIG. 1, for example, a process for exhibiting an anchor effect with respect to sealing resin1may be applied to a surface202, which is at another position separated by a further distance relative to the predetermined position of interconnection material2separated by the distance from the end surface of joining material5.

Surface202of interconnection material2is a position adjacent to surface201or a position close to surface201. Moreover, surface202of interconnection material2is located at the surface (surface A) thereof facing power semiconductor element4. The area of surface202is smaller than the total area of the interface between surface A of interconnection material2and the sealing resin. Examples of the process for exhibiting the anchor effect include a method for providing a rough surface of interconnection material2. Alternative examples of the process include a method for forming a hole or through hole in interconnection material2.

Next, the following describes modifications of power module PM. It should be noted that in each of the modifications, the same reference characters are given to the same members as those in the configuration of power module PM shown inFIG. 1, and are not repeatedly described unless required.

Here, the following describes a modification of the manner of connection of interconnection material2to power semiconductor element4. As shown inFIG. 2, interconnection material2is connected to power semiconductor element4with the end portion of interconnection material2being connected to joining material5. The end surface of interconnection material2is substantially flush with the end surface of joining material5.

As the clearance portion, in addition to clearance portion3, a clearance portion3ain which sealing resin1is continuously detached is formed to extend from the end surface of joining material5to a portion of the end surface of interconnection material2. Moreover, a portion (surface202) of the end surface of interconnection material2near clearance portion3ahas been through a process for increasing adhesion force between sealing resin1and interconnection material2. It should be noted that in order to provide clearance portion3aat the end surface of interconnection material2, an interconnection material having a thickness on the order of 0.1 mm to 1 mm (several mm) is applied, for example.

In power module PM according to the first modification, clearance portion3ais formed to extend from the end surface of joining material5to the portion of the end surface of interconnection material2. Also in the case where such a clearance portion3ais formed, stress can be relaxed at the interface between power semiconductor element4and sealing resin1since sealing resin1has been detached from interconnection material2and the like. Accordingly, sealing resin1is less likely to be detached from power semiconductor element4, thereby suppressing development of detachment of sealing resin1.

Here, the following describes a power module including a plurality of power semiconductor elements. As shown inFIG. 3, power module PM includes two power semiconductor elements4, for example. Interconnection material2is connected to bridge between two power semiconductor elements4by joining material5.

Although power module PM according to the second modification includes two power semiconductor elements4, clearance portion3is formed in each of two power semiconductor elements4. Accordingly, stress can be relaxed at the interface between sealing resin1and each of power semiconductor elements4. As a result, sealing resin1is less likely to be detached from power semiconductor element4, thereby suppressing development of detachment of sealing resin1.

As such, since clearance portion3is formed in each of power modules PM described above, stress can be relaxed. As described above, in clearance portion3, surface201of interconnection material2has been through the process for decreasing the adhesion force to sealing resin1. Here,FIG. 4shows an exemplary pattern of surface201in interconnection material2. As shown inFIG. 4, surface201is in the form of a frame having a width to surround a region (central rectangular portion) in which joining material5is located.

As described above, an exemplary process for decreasing adhesion force is a method for applying nickel (Ni) plating onto the region of interconnection material2corresponding to surface201. Moreover, an alternative exemplary process for decreasing adhesion force is a method for applying a parting agent by stencil printing or the like to the region of interconnection material2corresponding to surface201.

When the temperature is decreased to the room temperature after sealing resin1is cured, sealing resin1cannot withstand thermal stress resulting from the difference in linear thermal expansion coefficient at the interface between sealing resin1and surface201of interconnection material2having been through such a process, with the result that sealing resin1is detached from surface201. Therefore, by changing the area to be subjected to the process for decreasing the adhesion force, clearance portion3can be designed.

This process can be performed before connecting interconnection material2and circuit board6to power semiconductor element4. Hence, as compared with a case where the process is applied after finishing connecting the power semiconductor element to the circuit board and the interconnection material, the process can be applied to interconnection material2before connecting to the circuit board and the interconnection material, can be performed more simply, and is suitable for mass production.

Second Embodiment

Here, the following describes a first example of a power module to which an interconnection material having a plate-like portion and a projection is applied as an interconnection material electrically connected to the power semiconductor element.

As shown inFIG. 5, in power module PM, interconnection material2has the plate-like portion and projection203. Projection203of interconnection material2is electrically and mechanically connected, via joining material5, to the electrode formed on one surface of power semiconductor element4. It should be noted that since a configuration other than this is the same as that of power module PM shown inFIG. 1, the same reference characters are given to the same members and are not repeatedly described unless required.

As interconnection material2having the plate-like portion and projection203, for example, it is possible to apply an interconnection material2having a projection203formed by bending the plate-like portion as shown inFIG. 6 (a). Moreover, as shown inFIG. 6 (b), it is possible to apply an interconnection material2having a projection203formed by embossing the plate-like portion.

Also in power module PM described above, clearance portion3is formed between sealing resin1and each of the end surface of joining material5and the surface of interconnection material2so as to extend from the end surface of joining material5to the surface of interconnection material2, the surface of interconnection material2being located between the end surface and a position of interconnection material2separated by a distance from the end surface. Accordingly, stress is relaxed at the interface between power semiconductor element4and sealing resin1, with the result that sealing resin1is less likely to be detached from power semiconductor element4. Accordingly, detachment of sealing resin1can be suppressed from being developed.

Moreover, a process for exhibiting an anchor effect with respect to sealing resin1is applied to surface202, which is at another position separated by a further distance relative to the predetermined position of interconnection material2separated by the distance from the end surface of joining material5. This effectively prevents development of detachment of sealing resin1.

Next, the following describes a modification of power module PM described above. It should be noted that in each of the modifications, the same reference characters are given to the same members as those in the configuration of power module PM shown inFIG. 5orFIG. 2, and are not repeatedly described unless required.

As shown inFIG. 7, in a power module PM according to a first modification, as with the structure shown inFIG. 2described above, interconnection material2is connected to power semiconductor element4such that the end portion of interconnection material2is connected to joining material5.

Also in power module PM according to this first modification, clearance portion3is continuously formed between sealing resin1and each of the end surface of joining material5and the surface of interconnection material2so as to extend from the end surface of joining material5to the surface of interconnection material2, the surface of interconnection material2being located between the end surface and a position of interconnection material2separated by a distance from the end surface. Accordingly, stress can be relaxed at the interface between power semiconductor element4and sealing resin1, with the result that sealing resin1is less likely to be detached from power semiconductor element4. Accordingly, detachment of sealing resin1can be suppressed from being developed.

As shown inFIG. 8, as with the structure shown inFIG. 3described above, a power module PM according to a second modification includes two power semiconductor elements4, and interconnection material2is connected to bridge between two power semiconductor elements4by joining material5.

Also in power module PM according to the second modification, clearance portion3is formed in each of two power semiconductor elements4. Accordingly, stress can be relaxed at the interface between sealing resin1and each of power semiconductor elements4. As a result, sealing resin1is less likely to be detached from power semiconductor element4, thereby suppressing development of detachment of sealing resin1.

Third Embodiment

Here, the following describes a second example of the power module to which the interconnection material having the plate-like portion and the projection is applied as the interconnection material electrically connected to the power semiconductor element.

As shown inFIG. 9, in power module PM, interconnection material2has the plate-like portion and projection203. Projection203of interconnection material2is electrically and mechanically connected, via joining material5, to the electrode formed on one surface of power semiconductor element4. Particularly, in this interconnection material2, the plate-like portion and projection203are formed in one piece.

Interconnection material2is formed by casting or by applying a process such as grinding, for example. That is, projection203is solid. It should be noted that since a configuration other than this is the same as that of power module PM shown inFIG. 1, the same reference characters are given to the same members and are not repeatedly described unless required.

Also in power module PM described above, clearance portion3is continuously formed between sealing resin1and each of the end surface of joining material5and the surface of interconnection material2so as to extend from the end surface of joining material5to the surface of interconnection material2, the surface of interconnection material2being located between the end surface and a predetermined position of projection203of interconnection material2separated by a distance from the end surface. Accordingly, stress is relaxed at the interface between power semiconductor element4and sealing resin1, with the result that sealing resin1is less likely to be detached from power semiconductor element4. Accordingly, detachment of sealing resin1can be suppressed from being developed.

Moreover, a process for exhibiting an anchor effect with respect to sealing resin1is applied to surface202, which is at another position separated by a further distance relative to the predetermined portion of projection203of interconnection material2separated by the distance from the end surface of joining material5. This effectively prevents development of detachment of sealing resin1.

Next, the following describes a modification of power module PM described above. It should be noted that in the modification, the same reference characters are given to the same members as those in the configuration of power module PM shown inFIG. 9orFIG. 1, and are not repeatedly described unless required.

As shown inFIG. 10, as with the structure shown inFIG. 3described above, power module PM according to the modification includes two power semiconductor elements4, and interconnection material2is connected to bridge between two power semiconductor elements4by joining material5.

Also in power module PM according to this modification, clearance portion3is formed in each of two power semiconductor elements4. Accordingly, stress can be relaxed at the interface between sealing resin1and each of power semiconductor elements4. As a result, sealing resin1is less likely to be detached from power semiconductor element4, thereby suppressing development of detachment of sealing resin1.

Fourth Embodiment

Here, the following describes a third example of the power module to which the interconnection material having the plate-like portion and the projection is applied as the interconnection material electrically connected to the power semiconductor element.

As shown inFIG. 11, in power module PM, interconnection material2has a plate-like conductor204and projection203. Projection203of interconnection material2is electrically and mechanically connected, via joining material5, to the electrode formed on one surface of power semiconductor element4. Particularly, in this interconnection material2, plate-like conductor204and projection203are separate pieces.

Projection203includes: a block-like conductor10; and a joining material9for joining block-like conductor10to plate-like conductor204. It should be noted that since a configuration other than this is the same as that of power module PM shown inFIG. 1, the same reference characters are given to the same members and are not repeatedly described unless required.

Next, the following describes an exemplary method for manufacturing power module PM having interconnection material2described above. First, nickel (Ni) plating is applied to at least a portion of each of the six surfaces of block-like conductor10in total. Since nickel is wettable by a solder, an appropriate surface of block-like conductor10having the nickel plating applied thereto can be soldered to plate-like conductor204. Accordingly, block-like conductor10can be fixed to plate-like conductor204by joining material9composed of the solder.

Next, the surface of block-like conductor10opposite to its surface on which joining material9is disposed is electrically and mechanically connected to the electrode of power semiconductor element4via joining material5. Next, interconnection material2, power semiconductor element4, and the like are sealed with sealing resin1. On this occasion, since adhesion force of nickel to sealing resin1is weak, sealing resin1is intentionally detached from the side surface of block-like conductor10having the nickel plating applied thereto, thus obtaining clearance portion3. In this way, power module PM is manufactured.

Also in power module PM described above, clearance portion3is continuously formed between sealing resin1and each of the end surface of joining material5and the surface of interconnection material2so as to extend from the end surface of joining material5to the surface of interconnection material2, the surface of interconnection material2being located between the end surface and a position of projection portion203of interconnection material2separated by a distance from the end surface. Accordingly, stress is relaxed at the interface between power semiconductor element4and sealing resin1, with the result that sealing resin1is less likely to be detached from power semiconductor element4. Accordingly, detachment of sealing resin1can be suppressed from being developed.

Moreover, a process for exhibiting an anchor effect with respect to sealing resin1is applied to surface202of the plate-like portion204of interconnection material2, surface202being separated by a further distance relative to the predetermined position of projection203of interconnection material2separated by the distance from the end surface of joining material5. This effectively prevents development of detachment of sealing resin1.

Next, the following describes a modification of power module PM described above. It should be noted that in the modification, the same reference characters are given to the same members as those in the configuration of power module PM shown inFIG. 11orFIG. 1, and are not repeatedly described unless required.

As shown inFIG. 12, as with the structure shown inFIG. 3described above, power module PM according to the modification includes two power semiconductor elements4, and interconnection material2is connected to bridge between two power semiconductor elements4by joining material5.

Also in power module PM according to the modification, clearance portion3is formed in each of two power semiconductor elements4. Accordingly, stress can be relaxed at the interface between sealing resin1and each of power semiconductor elements4. As a result, sealing resin1is less likely to be detached from power semiconductor element4, thereby suppressing development of detachment of sealing resin1.

Fifth Embodiment

Here, the following describes a fourth example of the power module to which the interconnection material having the plate-like portion and the projection is applied as the interconnection material electrically connected to the power semiconductor element.

As shown inFIG. 13, in power module PM, interconnection material2has the plate-like portion and projection203. Projection203of interconnection material2is electrically and mechanically connected, via joining material5, to the electrode formed on one surface of power semiconductor element4.

In interconnection material2, the plate-like portion and projection203are formed in one piece. Particularly, the end portion (end surface) of joining material5for connecting projection203to power semiconductor element4exhibits a shape of fillet expanding from projection203to power semiconductor element4. It should be noted that since a configuration other than this is the same as that of power module PM shown inFIG. 1, the same reference characters are given to the same members and are not repeatedly described unless required.

Next, the following describes an exemplary method for manufacturing power module PM described above. First, in order for the end portion of joining material5to exhibit the shape of fillet, a positional relation is important between electrode401of power semiconductor element4joined to joining material5and position205of interconnection material2wet by joining material5.FIG. 14schematically shows a plan view showing the positional relation.

In order for the end portion of joining material5to exhibit the shape of fillet, first, the area of position205of interconnection material2wet by joining material5needs to be smaller than the area of electrode401. Next, a region of wet position205needs to be located in the region of electrode401.FIG. 14shows an exemplary positional relation, which satisfies such two conditions, between electrode401and wet position205.

In the positional relation satisfying these conditions, the end portion (end surface) of joining material5can have the shape of fillet by using, as joining material5, a material temporarily in liquid state during the process. Examples of such material include a solder. After forming the end portion of joining material5into the shape of fillet, interconnection material2, power semiconductor element4, and the like are sealed with sealing resin1, thereby manufacturing power module PM.

Since the end portion of joining material5exhibits the shape of fillet in power module PM, sealing resin1located at this portion has a round shape101reflecting the shape of fillet. The portion of sealing resin1with round shape101is located near a position at which sealing resin1is adhered to power semiconductor element4.

This provides a more increased stress relaxation effect at the interface between power semiconductor element4and sealing resin1, thereby suppressing further development of detachment of sealing resin1from clearance portion3toward the interface between power semiconductor element4and sealing resin1.

It should be noted that the power modules described in the above embodiments can be combined variously as required.

INDUSTRIAL APPLICABILITY

The present invention is used effectively for a power module in which a power semiconductor element and the like are sealed with a sealing resin.

REFERENCE SIGNS LIST