Semiconductor device

A semiconductor device includes a laminated substrate having a circuit board; a semiconductor chip fixed to the circuit board; a terminal having a leading end portion with a cylindrical shape and a wiring portion with a shape other than the cylinder, the leading end portion and the wiring portion being formed of one conductive member; and a joining material which electrically and mechanically connects the circuit board and the leading end portion.

TECHNICAL FIELD

The present invention relates to a semiconductor device.

BACKGROUND ART

A power semiconductor module which is one of semiconductor devices includes a laminated substrate, a semiconductor chip, a housing, and terminals. The laminated substrate is formed by laminating, for example, a circuit board, an insulating plate, and a metal plate in order. Also, the semiconductor chip is electrically and mechanically connected to one region of the circuit board by a joining material. Also, the housing houses a metal substrate and the semiconductor chip, and the inside of the housing is filled with a seal material. One end of each of the terminals is electrically and mechanically connected to each of electrodes and the circuit board, which are provided on the front surface of the semiconductor chip, by respective joining materials, and the other end of the terminals is led outside the housing. The joining materials are, for example, solder.

The power semiconductor module has roughly two types of terminals, and one of them is a main terminal. The main function of the main terminal is to cause a main current to flow by way of the semiconductor chip or the like. The other is a control terminal, which is also called a sense terminal. The main function of the control terminal is to input a control signal into the semiconductor chip and to lead a temperature detection signal.

The sectional area of a portion of the main terminal joined to the circuit board has a predetermined area necessary according to current rating. Also, from the viewpoint of securing reliability, the main terminal and the circuit board are soldered in a shape such that they can be sufficiently joined. Meanwhile, in the control terminal only a microcurrent flows therethrough or only a voltage is applied thereto. Because of this, the area of a portion of the control terminal joined to the front surface electrode of the semiconductor chip or to the circuit board has a predetermined area corresponding to the package shape of a product regardless of the current rating of the main current. The region of the front surface electrode of the semiconductor chip, or of the circuit board, which is joined to the terminal, has a larger area than the leading end of the terminal.

PTL 1 illustrates a terminal which is formed of a conductive plate and has a leading end folded in an L-shape. Also, PTL 2 describes a terminal which is formed of a wire pin and a cylindrical portion in which to insert the wire pin.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

When joining the terminal having the leading end folded in an L-shape and the circuit board, the leading end of the terminal is lapped on a solder paste applied to the circuit board and is heated. The solder melted by being heated coagulates in the vicinity of the leading end of the terminal due to surface tension.

However, there is a case in which one portion of the melted solder scatters and adheres to the side surface of the circuit board. This raises fear of causing insulation failure. Also, there is a case in which the melted solder comes into a state in which it spreads to the end portion of the circuit board. This raises fear that heat stress is generated due to the difference in linear expansion coefficient between the solder and the circuit board, and the circuit board separates from the insulating plate, when in a heat cycle test or heat shock test of the power semiconductor module.

As measures against the heretofore described insulation failure and separation, measures to space the joining position of the terminal from the end portion of the circuit board, and to sufficiently increase the area of the circuit board relative to the sectional area of the leading end of the terminal, are taken. However, the measures limit the degree of freedom of disposition of the circuit board.

The invention is to advantageously solve the heretofore described problems and has for its object to provide a semiconductor device which can prevent the separation and insulation failure between the circuit board and the insulating plate and can improve the degree of freedom of disposition of the circuit board.

Solution to Problem

A semiconductor device of an aspect of the invention includes a laminated substrate having a circuit board; a semiconductor chip fixed to the circuit board; a terminal having a leading end portion with a cylindrical shape and a wiring portion with a shape other than the cylinder, the leading end portion and the wiring portion being formed of one conductive member; and a joining material which electrically and mechanically connects the circuit board and the leading end portion.

Also, a semiconductor device of another aspect of the invention includes a laminated substrate having a circuit board; a semiconductor chip which includes electrodes on a front surface, and a rear surface fixed to the circuit board; terminals each having a leading end portion with a cylindrical shape and a wiring portion with a shape other than the cylinder, the leading end portion and the wiring portion being formed of one conductive member; and joining materials which electrically and mechanically connect the electrode and the leading end portion, respectively.

Advantageous Effects of Invention

According to the semiconductor device of the invention, it is possible to prevent the separation and insulation failure between the circuit board and the insulating plate, and it is possible to improve the degree of freedom of disposition of the circuit board.

DESCRIPTION OF EMBODIMENTS

Hereafter, a specific description will be given, while referring to the drawings, of embodiments of a semiconductor device of the invention.

A semiconductor device1of this embodiment shown in schematic sectional view inFIG. 1is an example of a power semiconductor module. The semiconductor device1includes a laminated substrate3, a semiconductor chip5, terminals7to9, and joining materials6. Furthermore, the semiconductor device1includes a base plate2, a frame body11, a seal material12, and a cover13.

The laminated substrate3includes an insulating plate3a, a metal plate3bprovided on one surface of the insulating plate3a, and circuit boards3cprovided on the other surface of the insulating plate3a. The insulating plate3aand the metal plate3bhave a substantially quadrangular shape in plan. The insulating plate3ais made of, for example, insulating ceramics, such as aluminum nitride, silicon nitride, or aluminum oxide, and the metal plate3band the circuit boards3care made of, for example, copper. As the laminated substrate3, it is possible to use a DCB (Direct Copper Bond) substrate or the like wherein the metal plate3band the circuit boards3care joined directly to the insulating plate3a. The metal plate3bis joined to the principal surface of the base plate2by a joining material4such as a solder.

The circuit boards3chave3c1and3c2, in which a predetermined circuit is formed, in the example shown in the drawing. The semiconductor chip5is joined to the circuit board3c1by the conductive joining material6, for example, a solder. The conductive joining material can be one type selected from a solder, a metal paste, and a conductive adhesive.

Electrodes are provided on the front surface and rear surface of the semiconductor chip5. Further, the electrode on the rear surface is electrically and mechanically connected to the circuit board3c1via a conductive joining material4such as a solder. “Being electrically and mechanically connected” is defined as including not only a case in which objects are joined directly to each other, but also a case in which objects are joined to each other via a conductive joining material, such as a solder or a metal sintered member, and the same applies in the following description.

The semiconductor chip5is specifically, for example, a Schottky barrier diode, a power MOSFET, or an IGBT (insulated gate bipolar transistor). The semiconductor chip5may be a silicon semiconductor, or may be a SiC semiconductor. When the semiconductor chip5is a silicon carbide (SiC) power MOSFET, the SiC power MOSFET, having a high breakdown voltage compared with a silicon semiconductor chip and being switchable at a high frequency, is most suitable as the semiconductor chip5of the semiconductor device of this embodiment. However, the semiconductor chip5is not limited to an IGBT or a power MOSFET, only has to be a combination of one or a plurality of semiconductor elements which can operate to switch.

In this embodiment, a description will be given, as an example, of a case in which the semiconductor chip5is an IGBT. In this case, the electrode on the rear surface of the semiconductor chip5is a collector electrode, while the electrodes on the front surface are an emitter electrode and a gate electrode.

The terminal7which is a main terminal is electrically and mechanically joined to the circuit board3c1by the conductive joining material6such as a solder. The terminal7is electrically connected to the collector electrode on the rear surface of the semiconductor chip5. Also, the terminal8which is a main terminal is electrically and mechanically connected to the emitter electrode on the front surface of the semiconductor chip5by the conductive joining material6such as a solder. Furthermore, the terminal9which is a control terminal to be electrically connected to the gate electrode of the semiconductor chip5is electrically and mechanically connected to the circuit board3c2by the conductive joining material6such as a solder. The circuit board3c2and the gate electrode of the semiconductor chip are electrically connected by a bonding wire10. That is, in this embodiment, the terminal7is a collector terminal, the terminal8is an emitter terminal, and the terminal9is a gate terminal.

The metallic base plate2for heat release is made of a metal with a good heat conductivity, for example, copper, and has a substantially quadrangular shape in plan.

The frame body11made of a resin is bonded to the peripheral edge of the base plate2by an unshown adhesive. Also, the cover13is fixed to the top portion of the frame body11. The base plate2, the frame body11, and the cover13form a housing of the semiconductor device1. Further, the laminated substrate3and the semiconductor chip5are housed in the housing, and the housing is filled with the seal material12which enhances insulation.

FIGS. 2(A)-2(D)show a front view (FIG. 2(A)), side view (FIG. 2(B)), and plan view (FIG. 2(C)) of each terminal7to9. Also,FIG. 2(D)is a development view of each terminal7to9before leading end portion formation.

The terminals7to9are each formed of a leading end portion20and a wiring portion21. The leading end portion20is electrically and mechanically connected to each of the circuit boards3cand the front surface electrode of the semiconductor chip5using the joining material6. Also, the wiring portion21has a function to install electrical wiring to a predetermined portion of the semiconductor device1from the portion of the wiring portion21connected to the leading end portion20. Further, the leading end portion20has a cylindrical shape, and the wiring portion21has a shape (in this embodiment, a plate-like shape) other than a cylindrical shape. The leading end portion20has a side surface20a, which is continuous with the wiring portion21, and side surfaces20band20cperpendicular to the side surface20a. Further, a gap20gextending in an axial direction of the cylinder is disposed between the side surface20band the side surface20c. That is, the terminals7to9are each such that the leading end portion20and the wiring portion21are formed by one conductive member. In this embodiment, as can be seen from the development view of (D) ofFIG. 2, one conductive plate is folded along folding lines L1and L2to dispose the side surfaces20a,20b, and20cand gap20g, thus forming the leading end portion20of the cylindrical shape. As shown inFIG. 2(C), the leading end portion20has an approximately U-shape in horizontally cross-section having three side surfaces. In other words, a section of the leading end portion20perpendicular to the axis of the cylinder has a quadrangular, more specifically, rectangular shape with one side open.

The gap20gextends in the axial direction of the cylinder of the leading end portion20. Further, the gap20gis provided in a portion opposite to the side surface20awhich is the portion of the leading end portion20linked to the wiring portion21.

The material of the terminals7to9is a copper plate and is plated with nickel as needed. As the terminals7-9, it becomes easy to procure the material if using the same material as that of a conductive plate, specifically, a lead which is used in a common power semiconductor module. Because of this, it is possible to manufacture the terminals7to9at a low cost.

A description will be given, usingFIG. 3, of working effects of each terminal7to9(herein, the terminal9which is the control terminal) having the leading end portion20. When joining the terminal9, the joining material6is heated with a space c of on the order of 0.5 to 1.0 mm between the circuit board3c2and the leading end of the terminal9. The melted joining material6coagulates due to surface tension and comes into contact with the leading end of the terminal9. As the leading end portion20is cylindrical, the melted joining material6is drawn by capillarity into the cylindrical leading end portion20. Further, when the melted joining material6is cooled and solidified, a fillet6ais formed between the circuit board3c2and the leading end of the terminal9. The area taken up by the joining material6on the circuit board3c2is the sum of the portion surrounded by the leading end portion20and the fillet6a. The area is small compared with the case when using a terminal, described in PTL 1, which has a leading end folded in an L-shape. Consequently, as the melted joining material6does not spread to the end portion of the circuit board3c2, it is possible to prevent the circuit boards3cfrom separating from the insulating plate3a. Also, as it is possible to prevent one portion of the melted joining material6from scattering and adhering to the side surface at the end portion of the circuit board3c, it is possible to prevent insulation failure.

Also, as the leading end portion20has a simple structure compared with a cylindrical portion described in PTL 2, it is possible to reduce the cost of members. Furthermore, it is easy to fold the leading end portion20, and it is possible to reduce the number of steps compared with the process of soldering the cylindrical portion described in PTL 2 in advance and furthermore inserting a wire pin, and thus possible to reduce manufacturing costs.

Still furthermore, in the technology described in PTL 2, as a problem arises in inserting the wire pin when too much melted joining material is pulled into the cylindrical portion, it is necessary to strictly control the amount of joining material. Meanwhile, in this embodiment, as there is no particular problem even when too much melted joining material6is drawn into the cylindrical leading end portion20, it is not necessary to strictly control the amount of joining material. Because of this, it is possible to reduce the manufacturing costs. In order to prevent the joining material6overflowing from the leading end portion20even when the joining material6is in excess, it is preferable to make the height of the leading end portion20higher than the height of the joining material6drawn into the leading end portion20.

It is preferable to set the space c between the circuit board3cand the leading end of the terminal9to on the order of 0.5 to 1.0 mm because the joining material6in the vicinity of the leading end of the terminal9can form the fillet6aof a good shape.

By the leading end portion20having the gap20g, the joining material6melted when heated can move into and out of the cylindrical leading end portion20through the gap20g. Because of this, it is possible to form the fillet6alarge in width and height compared with the case when the leading end portion20has no gap20g. Consequently, it is possible to enhance the joining strength of the joining material6, and thus possible to improve joining reliability.

Also, as shown inFIG. 1, end portions of the wiring portions21of the terminals7to9on the opposite side to the leading end portions20can also be directly led outside the housing of the semiconductor device1. This is because as the terminals7to9are rigidly joined by the cylindrical leading end portions20, it does not happen that the junctions separate even when stress from outside is applied to the terminals7to9. As the need for dedicated external lead-out terminals is eliminated by directly leading the wiring portions21outside the housing, it is possible to reduce the manufacturing costs.

Also, in this embodiment, the wiring portions21have a plate-like shape, but may have any shape other than a cylindrical shape as long as it is possible to easily wire the wiring portions to predetermined portions. In this embodiment, the reason for the wiring portions21having a shape other than a cylindrical shape is that as a cylindrical shape is difficult to bend easily, it is difficult for the wiring portions in cylindrical shape to be wired to the predetermined portions. Because of this, a plate-like shape, a rod-like shape, a wire-like shape, or the like, which is easy to bend is suitable as the shape of the wiring portions21.

In this embodiment, the semiconductor device1is formed using the frame body11, seal material12, and cover13. Meanwhile, it is also possible to form the semiconductor device by sealing the semiconductor chip and the like by insert molding using a thermosetting resin. By so doing, it becomes possible to reduce the size of the semiconductor device.

Also, in this embodiment, a solder is used as the joining material6, but any joining material may be used as long as it is a conductive joining material in a liquid state in which the fillet6acan be formed at the leading end portion20. As the joining material6, it is also possible to use, for example, a metal paste or a conductive adhesive.

FIG. 4shows a plan view of each terminal7to9of Embodiment 2. This is a diagram corresponding toFIG. 2(C)of Embodiment 1.

In the terminals7to9of the semiconductor device of Embodiment 2, the angle to which the side surfaces20band20care bent is increased to reduce the gap20gbetween both side ends. By so doing, the shape of the leading end portion20in section perpendicular to the axis of the cylinder has an approximately trapezoidal shape. Other structures are the same as those of Embodiment 1 described usingFIGS. 2(A)-2(D)and3. The terminals7to9of this embodiment have the same working effects as the terminals7to9of Embodiment 1. Still furthermore, as it is possible to reduce the junction area compared with in Embodiment 1, there is effectiveness when joining each terminal to a narrow region.

Each of the terminals7to9of the semiconductor device of Embodiment 3 has a cylindrical leading end portion20of an approximately rectangular shape in horizontally cross-section and a wiring portion21of a plate-like shape. The leading end portion20has a side surface20acontinuous with the wiring portion21, side surfaces20band20cperpendicular to the side surface20a, and side surfaces20dand20eperpendicular to and shorter in width than the side surfaces20band20c. Further, a gap20gextending in an axial direction of the cylinder is disposed between the side surface20dand the side surface20e. As can be seen from the development view ofFIG. 5(C), one conductive plate is folded along folding lines L1to L4to dispose the side surfaces20ato20eand gap20g, thus forming the cylindrical leading end portion20.

The terminals7to9of Embodiment 3 have the same structures as the terminals7to9of Embodiments 1 and 2, except that the leading end portions20have different shapes in horizontally cross-section. Further, the terminals7to9of this embodiment have the same working effects as the terminals7to9of Embodiments 1 and 2. Furthermore, in this embodiment, as the area of the side surfaces of the leading end portion20is wide compared with in Embodiments 1 and 2, the capillary action of the melted joining material6becomes likely to occur.

The terminals7to9are not limited to have the leading end portions20of the rectangular and trapezoidal shapes in horizontally cross-section described in Embodiments 1 to 3, and can be modified in various ways. The shape in horizontally cross-section can be made, for example, polygonal or circular. The inner diameter of the leading end portion20is an inner diameter such that the melted joining material6can be drawn by capillarity.

Each of the terminals7to9of the semiconductor device of Embodiment 4 has a cylindrical leading end portion20of an approximately rectangular shape in horizontally cross-section, and a wiring portion21of a plate-like shape, in the same way as the terminals7to9of Embodiment 3. Furthermore, in this embodiment, as shown in the side view ofFIG. 6(B)and the development view ofFIG. 6(C), a plurality of, in the example shown in the drawings, three, slits20sextending in an axial direction of the cylinder is disposed one in each of respective portions of the side surface20a, side surface20b, and side surface20con the side which is connected by the joining material6.

That is, the terminals7to9of Embodiment 4 have the same structures as the terminals7to9of Embodiment 3, except that the slits20sare disposed. Consequently, the terminals7to9of Embodiment 4 have the same effects as the terminals7to9of Embodiment 3. Furthermore, in the terminals7to9of Embodiment 4, as the slits20sare disposed in the leading end portion20, the joining material6melted when heated can move into and out of the cylindrical leading end portion20through the slits20s. Because of this, a fillet6alarge in width and height is formed compared with when the leading end portion has no slit20s.

FIG. 7(A)shows a sectional view of Embodiment 3 having no slit20s, andFIG. 7(B)shows a sectional view of Embodiment 4 having the slits20s. To compareFIG. 7(A)andFIG. 7(B), the fillet6aof the joining material6is larger in Embodiment 4 than in Embodiment 3. Consequently, in Embodiment 4, as it is possible to further enhance the joining strength of the terminals7to9, there is effectiveness when the joining strength is needed. Also, in Embodiment 3, as it is possible to narrow the width of the joining material6, there is effectiveness in narrowing the area of installment of the joining material6, for example, when it is not possible to take up a wide area for electrodes and circuit boards.

Also, in this embodiment, the slits20sare disposed one in each of the opposing side surfaces20band20c. By disposing two slits20s, one in each of mutually opposing positions, in this way, it is possible to form the fillet6aof the joining material6in an axisymmetric shape as shown inFIG. 7(B). Because of this, in the leading end portion20, as it is possible to equalize the force with which the opposing side surfaces are joined together, thus improving reliability, effectiveness is increased. As previously described, the gap20galso has the same function as the slits20s. Because of this, it is also effective that the gap20gand the slit20sare disposed in mutually opposing positions, as shown in this embodiment.

The shape in horizontally cross-section of the leading end portions of the terminals7to9having the slits20sis not limited to the rectangle shown inFIGS. 6(A)-6(C), and can also be applied to the trapezoid shown inFIG. 3or any other shape in horizontally cross-section, such as a polygon or a circle.

Reference Example

FIG. 8is a plan view when an L-shaped terminal108described in PTL 1 is used for connection to a semiconductor chip105.

The L-shaped terminal108is electrically and mechanically connected to an electrode105eon the front surface of the semiconductor chip105by a conductive joining material (not shown). Also, the front surface electrode disposed on the semiconductor chip5is formed in a rectangular shape.

For the semiconductor chip105, there is a case in which the junction of the chip rear surface and a circuit board by a joining material, and the junction of the front surface and a terminal108by a joining material, are implemented by the same heating process. In this case, as the joining material on the rear surface side of the semiconductor chip is also melted, there is fear that when the shape of the leading end of the terminal108is relatively small compared with the electrode105e, the semiconductor chip105rotates on the spot.

FIG. 9is a plan view when a terminal8of Embodiment 5 is used for connection to a semiconductor chip5.

In Embodiment 5, one of the sides of the terminal8which form side surfaces20a,20b, and20cis made longer than one side5e1(a short side) or5e2(a long side) of a rectangular electrode5eon the front surface of the semiconductor chip5. In other words, the side surface20b(20c) which is the long side of the terminal8is made longer than the short side5e1of the electrode5e. By so doing, it is possible to prevent the semiconductor chip5from rotating on the spot. That is, this embodiment enables self-alignment of the semiconductor chip5.

Heretofore, a specific description has been given, using the drawings and embodiments, of the semiconductor device of the invention, but the semiconductor device of the invention is not limited to the descriptions in the embodiments and drawings, and can be variously modified without departing from the scope of the invention. For example, the leading end portion20is not limited to be provided perpendicular to the front surface of the circuit board3cor semiconductor chip5, but may have a predetermined angle. Also, a solder paste may be adhered in advance to the leading end portion20.

REFERENCE SIGNS LIST