SEMICONDUCTOR DEVICE

A semiconductor device includes a semiconductor element and a terminal substrate. The semiconductor element has a main electrode and a control electrode on a first main surface. The terminal substrate has a bonding terminal to which a wire is to be bonded on a front surface and a relay terminal on a back surface. The bonding terminal and the relay terminal are electrically connected to each other. The bonding terminal has an area larger than an area of the control electrode. The terminal substrate is bonded to the semiconductor element so that the relay terminal and the control electrode are in contact with each other. The terminal substrate has a step on the back surface, and a side surface of the semiconductor element is in contact with the step.

TECHNICAL FIELD

The present disclosure relates to a semiconductor device.

BACKGROUND

There is a semiconductor device in which a main electrode and a control electrode are provided on one main surface of a semiconductor element. Such a semiconductor device is, for example, a power semiconductor device for power conversion. In the power semiconductor device, since a current, which is smaller than a current flowing through the main electrode, flows through the control electrode, the area of the control electrode is smaller than the area of the main electrode. In such a semiconductor device, a metal block is connected to the main electrode, and a wire is bonded to the control electrode.

For example, there is a semiconductor device having a wiring sheet attached to one main surface of a semiconductor element. The wiring sheet has an electrode terminal connected to a main electrode and a control terminal connected to a control electrode on one of main surfaces.

SUMMARY

The present disclosure describes a semiconductor device including a semiconductor element and a terminal substrate. According to an aspect, the semiconductor element has a main electrode and a control electrode on a first main surface. The terminal substrate has a bonding terminal to which a wire is to be bonded on a front surface and a relay terminal on a back surface. The bonding terminal and the relay terminal are electrically connected to each other. The bonding terminal has an area larger than an area of the control electrode. The terminal substrate is bonded to the semiconductor element so that the relay terminal and the control electrode are in contact with each other. The terminal substrate has a step on the back surface, and a side surface of the semiconductor element is in contact with the step.

DETAILED DESCRIPTION

To begin with, a relevant technology will be described only for understanding the embodiments of the present disclosure.

For example, a semiconductor device, such as a power semiconductor device for power conversion, has a main electrode and a control electrode on one surface of a semiconductor element. Since a smaller current flows in the control electrode than in the main electrode, an area of the control electrode is smaller than an area of the main electrode. In such a semiconductor device, a metal block is connected to the main electrode, and a wire, such as a bonding wire is bonded to the control electrode. The bonding wire is often made of aluminum, and has a diameter of about 500 μm.

As another example, there is a semiconductor device having a wiring sheet attached to a main surface of a semiconductor element on one side. The wiring sheet has an electrode terminal connected to a main electrode and a control terminal connected to a control electrode on one of main surfaces. A copper member is provided inside the wiring sheet, and one end of the copper member is connected to the control terminal. The other end of the copper member is connected to a control electrode terminal, and the control electrode terminal extends out from the wiring sheet. Since the control electrode of the semiconductor element is connected to the copper member through the control terminal on the wiring sheet rather than the wire, the distance between the main electrode and the control electrode can be shortened. For example, a flexible printed circuit board is used for the wiring sheet.

Since only a smaller current flows through the control electrode, the control electrode may be significantly smaller than the main electrode in terms of current capacity. However, in such a semiconductor device described above, the wire (bonding wire) is bonded to the control electrode. In order to bond the wire, the control electrode needs a larger area than the cross-sectional area of the wire. However, if the control electrode is enlarged only for the bonding of the wire, an area of the main surface of the semiconductor element will be enlarged unnecessarily. If the area of the control electrode can be reduced, the area of the main surface of the semiconductor element, that is, the external dimensions of the semiconductor element can be reduced. Since SiC substrates and GaN substrates, which have been attracting attention in recent years, are expensive, the reduction of the area of the main surface results in the reduction of the cost of the semiconductor device.

In the semiconductor device having the wiring sheet, the area of the control electrode can be reduced, and the area of the main surface of the semiconductor element can be reduced accordingly. However, if a flexible wiring sheet is used as the wiring sheet, it is difficult to align the terminal of the wiring sheet to the control electrode of the semiconductor element. The control electrode of the semiconductor element requires an area large enough to allow for a positional error with respect to the terminal on the wiring sheet.

The present disclosure provides a semiconductor device which is capable of reducing the area of a control electrode.

According to an aspect of the present disclosure, a semiconductor device includes a semiconductor element and a terminal substrate. The semiconductor element is provided with a main electrode and a control electrode on a first main surface. The terminal substrate has a bonding terminal to which a wire is to be bonded on a front surface thereof, and a relay terminal on a back surface thereof. The bonding terminal and the relay terminal are electrically connected to each other. The terminal substrate is bonded to the semiconductor element so that the relay terminal is in contact with the control electrode. The bonding terminal has an area larger than the area of the control electrode. Further, the terminal substrate is formed with a step on the back surface, and a side surface of the semiconductor element is in contact with the step.

Since the bonding terminal to which a wire is bonded is provided on the board separate from the semiconductor element, that is, on the terminal substrate, the control electrode on the main surface can be made smaller. Since the side surface of the semiconductor element is brought into contact with the step on the back surface of the terminal substrate, the position of the terminal substrate relative to the semiconductor element can be determined accurately. Therefore, the positional error between the control electrode of the semiconductor element and the relay terminal of the terminal substrate can be reduced, and the control electrode can be made smaller accordingly.

For example, the step may be configured as follows. The terminal substrate has a thin plate portion including the relay terminal and a thick plate portion including the bonding terminal. The thickness of the thin plate portion is smaller than the thickness of the thick plate portion. The step is provided by the boundary between the thin plate portion and the thick plate portion on the back surface of the terminal substrate. The thin plate portion is bonded to the semiconductor element. The back surface of the thick plate portion of the terminal substrate may be flush with a second main surface of the semiconductor element. If there is a flat surface under the semiconductor element and the thick plate portion, both the semiconductor element and the thick plate portion can be supported by the flat surface. In such a case, therefore, the semiconductor element and the thick plate portion will not shift in the thickness direction when the wire is bonded to the bonding terminal.

As another example, a protrusion may be provided on the back surface of the terminal substrate, and the protrusion may form the step.

Details and further improvements provided by the present disclosure will be further explained hereinafter.

First Embodiment

A semiconductor device2of a first embodiment will be described with reference to the drawings.FIG.1is a perspective view of the semiconductor device2.FIG.2is an exploded perspective view of the semiconductor device2. The semiconductor device2is a device in which a semiconductor element20is sealed in a resin package10. InFIG.1, the semiconductor element20is covered by the resin package10and is therefore not visible.FIG.2is the exploded perspective view of the semiconductor device2in which illustration of the resin package10is omitted, and in a state where a first heat dissipation plate14is removed.

The semiconductor element20is a switching element for power conversion, such as an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field effect transistor (MOSFET). The semiconductor element20is thus generally referred to as a power semiconductor element. The semiconductor element20has a first main surface20aas a main surface on one side. A first main electrode21and a plurality of control electrodes23(seeFIG.5) are arranged at the first main surface20aof the semiconductor element20. InFIG.2, the control electrodes23are not visible as being hidden behind the terminal substrate30. The semiconductor element20has a second main surface20bon the other side, as another main surface. A second main electrode22is arranged at the second main surface20bof the semiconductor element20. The first main electrode21and the second main electrode22are connected to a source and a drain of the switching element, and thus large currents (for example, 10 amperes or more) flow through the first main electrode21and the second main electrode22.

The lower surface of a copper block17is bonded to the first main electrode21on the first main surface20a, and a first heat dissipation plate14is bonded to the upper surface of the copper block17. A first main terminal11extends from the edge of the first heat dissipation plate14. The second main electrode22(seeFIG.5) is arranged at the second main surface20b, and a second heat dissipation plate15is bonded to the second main surface20bincluding the second main electrode22. A second main terminal12extends from the edge of the second heat dissipation plate15.

As shown inFIG.1, the first heat dissipation plate14is exposed on a wide surface of the resin package10on one side, and the first main terminal11extends outward from the resin package10. Although the second heat dissipation plate15is not visible inFIG.1, the second heat dissipation plate15is also exposed on a wide surface of the resin package10on the other side, and the second main terminal12extends outward from the resin package10. The first heat dissipation plate14has functions as an electric conduction path between the first main electrode21of the semiconductor element20and the first main terminal11as well as a heat sink. Similarly, the second heat dissipation plate15has functions as an electric conductive path between the second main electrode22of the semiconductor element20and the second main terminal12as well as a heat sink.

Although not visible inFIGS.1and2, a plurality of control electrodes23are exposed on the first main surface20aof the semiconductor element20together with the first main electrode21. A terminal substrate30is mounted on the semiconductor element20, and a plurality of bonding terminals33are exposed on a front surface30aof the terminal substrate30. As will be described in detail later, each of the plurality of control electrodes23of the semiconductor element20is electrically connected to each of the bonding terminals33. One end of each bonding wire16is connected to each bonding terminal33, and the other end of each bonding wire16is connected to each control terminal13. Note that the terms “front surface” and “back surface” of the terminal substrate30are used for convenience to distinguish a pair of surfaces facing in opposite directions from each other. The terms “front surface” and “back surface” may be replaced with “one surface” and “the other surface” as a pair of surfaces facing in opposite directions.

As shown inFIG.1, the plurality of control terminals13extend outward from the resin package10. The plurality of control electrodes23arranged on the first main surface20aof the semiconductor element20are connected to a gate, a sense emitter, a temperature sensor, and the like inside the semiconductor element20. The bonding wire16has electrical conductivity. The plurality of control electrodes23of the semiconductor element20are electrically connected to the plurality of control terminals13via the terminal substrate30and the plurality of bonding wires16.

Although the semiconductor element20and the terminal substrate30are covered by the resin package10, external devices can be electrically connected to the first main electrode21, the control electrodes23and the like of the semiconductor element20via the main terminals11and12and the control terminals13.

FIG.3shows a perspective view in which the terminal substrate30is separated from the semiconductor element20. As described above, the plurality of control electrodes23are arranged on the first main surface20aof the semiconductor element20together with the first main electrode21. As described above, the control electrodes23are connected to the gate, the sense emitter, the temperature sensor and the like, and through which only smaller currents than the current flowing through the main electrode flow. Therefore, the area of the control electrode23is significantly smaller than the area of the first main electrode21.

For convenience of explanation, the surface of the terminal substrate30facing a +Z direction will be referred to as a front surface30a, and the surface facing a −Z direction will be referred to as a back surface30b. In a right upper area inFIG.3, the terminal substrate30, which is turned upside down from the terminal substrate30shown on the left side, is shown.

FIG.4is a plan view of the semiconductor device2, andFIG.5is a cross-sectional view taken along a line V-V inFIG.4. However, inFIG.4, illustrations of the resin package10, the first heat dissipation plate14, and the copper block17are omitted. InFIG.5, illustration of the internal structure of the semiconductor element20is omitted. The structure of the terminal substrate30will be described in detail with reference toFIGS.3to5.

The plurality of bonding terminals33are arranged on the front surface30aof the terminal substrate30, and the plurality of relay terminals34are arranged on the back surface30bof the terminal substrate30. The plurality of bonding terminals33are correspondingly and electrically connected to the plurality of relay terminals34inside the terminal substrate30.

The terminal substrate30includes a thin plate portion31having a small thickness and a thick plate portion32having a large thickness. The thickness of the thin plate portion31is smaller than the thickness of the thick plate portion32. The plurality of relay terminals34are arranged on the back surface30bof the thin plate portion31. On the back surface30bof the terminal substrate30, the boundary between the thin plate portion31and the thick plate portion32forms a step35.

The terminal substrate30is bonded to the semiconductor element20such that each of the plurality of relay terminals34is in contact with and is electrically connected to each of the plurality of control electrodes23. In this case, the terminal substrate30is fixed to the semiconductor element20so that a side surface20cof the semiconductor element20abut to the step35, in particular, to the side surface of the step (seeFIG.5). In other words, the corner between the first main surface20aand the side surface20cof the semiconductor element20is in contact with the corner of the step35.

Each of the plurality of relay terminals34is arranged so as to face each of the plurality of control electrodes23when the side surface20cof the semiconductor element20is in contact with the step35. When the terminal substrate30is attached to the semiconductor element20so that the side surface20cis in contact with the step35, each of the plurality of relay terminals34comes into contact with each of the plurality of control electrodes23and is electrically connected. The step35serves to accurately position the terminal substrate30with respect to the semiconductor element20at a target position.

The bonding wire16is generally made of aluminum and has a diameter of about 500 micrometers (μm). As shown inFIG.5, since the tip of the bonding wire16(i.e., the tip bonded to the bonding terminal33) is melted by heat, the tip is larger than the diameter. As best shown inFIGS.3through5, the bonding terminal33has a sufficient area to secure the bonding wire16. In other words, the area of the tip of the bonding terminal33is larger than the cross-sectional area of the bonding wire16. On the other hand, since the terminal substrate30is accurately positioned with respect to the semiconductor element20by the step35, the control electrode23and the relay terminal34are reliably in contact with each other even if their areas are small. The area of the bonding terminal33is significantly larger than the areas of the control electrode23and the relay terminal34. In other words, the areas of the control electrode23and the relay terminal34are smaller than the area of the bonding terminal33.

In the semiconductor device2of the first embodiment, the terminal substrate30ensures the bonding terminals33having sufficient areas for bonding the bonding wires16, as well as enables to reduce the control electrodes23provided on the first main surface20aof the semiconductor element20in size. As a result, the main surface of the semiconductor element20can be reduced in size. That is, the semiconductor element20can be reduced in size.

As shown inFIG.5, the bonding terminals33provided on the front surface30aof the terminal substrate30and the relay terminals34provided on the back surface30bof the terminal substrate30are connected to each other through conductive patterns38provided inside the terminal substrate30.

Most part of the bonding terminal33is arranged in the thick plate portion32of the terminal substrate30, and the relay terminal34is arranged in the thin plate portion31. The thin plate portion31is bonded to the first main surface20aof the semiconductor element20. As shown inFIG.5, the back surface30bof the thick plate portion32is flush with the second main surface20bof the semiconductor element20, and both the back surface30band the second main surface20bare in contact with the flat second heat dissipation plate15. The back surface30bof the terminal substrate30is in contact with the second heat dissipation plate15in a state where the terminal substrate30is bonded to the semiconductor element20. Therefore, when the bonding wires16are bonded to the bonding terminals33, the terminal substrate30will not be displaced relative to the semiconductor element20.

FIG.6shows a perspective view of a terminal substrate130as a first modification. The terminal substrate130has a step135on a back surface130b, and the step135has side surfaces135aand135balong two directions. The side surface135aand the side surface135bare orthogonal to each other. The side surface135aand the side surface135bof the step135face the −X direction and the −Y direction of the coordinate system in the drawing, respectively. When the terminal substrate130is attached to the semiconductor element20, the side surfaces135aand135bof the step135abut against the side surfaces20cand20dof the semiconductor element20, respectively. The side surface20dintersects the side surface20c. Since the terminal substrate130has the step135with the side surfaces135aand135balong the two directions, the terminal substrate130can be accurately positioned with respect to the semiconductor element20in two orthogonal directions.

Instead of having the second side surface135bon the step135, the second heat dissipation plate15may have a protruding guide. The surface of the terminal substrate30and the surface of the semiconductor element20of the first embodiment respectively facing the Y direction are pressed against the protruding guide. Thus, the terminal substrate30can be accurately positioned with respect to the semiconductor element20also in the Y direction.

A terminal substrate230as a second modification will be described with reference toFIGS.7and8.FIG.7is a perspective view of the terminal substrate230and the semiconductor element20.FIG.8is a cross-sectional view of a semiconductor device202to which the terminal substrate230is attached. In the upper right area ofFIG.7, the terminal substrate230is illustrated as a perspective view turned upside down from the one shown on the left side.FIG.7corresponds toFIG.3, andFIG.8corresponds toFIG.5.

The terminal substrate230includes a plurality of protrusions231, instead of having the thick plate portion32of the terminal substrate30of the first embodiment. In the right upper area ofFIG.7, the terminal substrate230is illustrated so that the back surface230bfaces upward. The plurality of bonding terminals33are arranged on a front surface230aof the terminal substrate230, and the plurality of relay terminals34are arranged on the back surface230b. The bonding terminals33are correspondingly and electrically connected to the relay terminals34through the conductive patterns38inside the terminal substrate230.

The plurality of protrusions231are provided on the back surface230bof the terminal substrate230. The side surface of the protrusion231serves as the step35of the terminal substrate30of the first embodiment. More precisely, the height difference between the back surface230bof the terminal substrate230and the tip surface of the protrusion231corresponds to the step.

When the terminal substrate230is attached to the semiconductor element20, the side surface of the protrusion231, which corresponds to the side surface of the step, is brought into contact with the side surface20cof the semiconductor element20. By bringing the side surface of the protrusion231into contact with the side surface20cof the semiconductor element20, the terminal substrate230can be accurately positioned relative to the semiconductor element20in the X direction.

Other features regarding the semiconductor devices2(202) of the embodiments will be described hereinafter. The terminal substrate30(130,230) is made of the same material as the resin package10covering the semiconductor element20. The material of the resin package10is typically polyimide or polyamide. By making the terminal substrate30(130,230) from the same material as the resin package10, the stress generated near the boundary between the resin package10and the terminal substrate30(130,230) can be reduced when the resin package10is formed by injection molding.

The points to be noted regarding the techniques of the embodiments described above will be described. A plurality of terminal substrates may be attached to one semiconductor element. A plurality of control electrodes may be dispersedly arranged at a plurality of locations on the first main surface of the semiconductor element20.

Although specific examples of the present disclosure have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above. The technical elements described in the present description or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the present description at the time of filing. In addition, the techniques illustrated in the present specification or the drawings can achieve multiple purposes at the same time, and achieving one of the purposes itself has technical usefulness.