Power semiconductor device

A power semiconductor device includes: a mold unit that includes a power semiconductor element, a base plate, and a mold unit, the power semiconductor element being mounted on one surface of the base plate, a convex portion being formed on an other surface of the base plate, the convex portion including a plurality of grooves, the mold unit having a mold resin with which the power semiconductor element is sealed in such a manner as to expose the convex portion; a plurality of radiation fins inserted into the grooves, respectively, and fixedly attached to the base plate by swaging; and a metal plate that includes a opening into which the convex portion is inserted, the metal plate being arranged between the mold unit and the radiation fins with the convex portion inserted into the opening, wherein the metal plate includes a protrusion that protrudes from an edge of the opening and that digs into a side surface of the convex portion when the convex portion is inserted into the opening.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2012/069487 filed Jul. 31, 2012, the contents of which are incorporated herein by reference in their entirety.

FIELD

The present invention relates to a power semiconductor device.

BACKGROUND

Conventionally, when a heat sink is attached for cooling electronic components (power semiconductor elements) that generate a large amount of heat such as a CPU (central processing unit) and a power transistor, application of thermal grease is widely performed to fill a minute gap between a contact surface of the electronic components and that of the heat sink to improve heat dissipation performance.

The thermal conductivity of the thermal grease is quite lower than those of metals. Accordingly, a radiation-fin-integrated power semiconductor device having radiation fins integrated with a base plate of a metallic part of the power semiconductor device without using the thermal grease is also realized to further improve the heat dissipation performance. In the radiation-fin-integrated power semiconductor device, grooves for joining the radiation fins are provided in the base plate, resin molding is performed in a state of exposing a part of the surface of the base plate including a portion in which these grooves are formed, and the radiation fins are inserted into the grooves of the base plate and then swaged to be fixedly attached to the grooves, thereby integrating the base plate with the radiation fins to improve the heat dissipation performance.

In relation to the power semiconductor device adapted to improve the heat dissipation performance, it is known that radiation noise from power semiconductor elements and malfunction is suppressed by inserting a metal plate between the radiation fins and the base plate and by causing this metal plate to function to connect the power semiconductor device to an earth potential (see Patent Literature 1).

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

In the conventional technique, heating and cooling is carried out at a time of sealing the power semiconductor elements with resin. This often causes a module of the power semiconductor device to be completed in a warped state or causes the metal plate to be inserted itself to be warped. Therefore, the conventional technique has a problem that a gap is generated between the metal plate and the base plate, which increases the electrical resistance between the metal plate and the base plate. Furthermore, an oxide film is formed in the atmosphere on the surface of the base plate that is a metal, and the oxide film on the metal is higher than the metal itself in the electrical resistance. With the conventional technique, an electrical contact between the metal plate and the base plate is realized by placing the metal plate between the radiation fins and the base plate. Accordingly, the metal plate and the base plate are electrically connected to each other via the oxide film formed on the surface of the base plate except for minute regions where the oxide film on the surface of the base plate is damaged as a result of the contact of the metal plate with the base plate and where the metal is exposed. For this reason, even if neither the metal plate nor the base plate is warped and the base plate comes in surface contact with the metal plate, a ratio of portions that are made conductive as a result of the contact of the metals is low, disadvantageously resulting in a high electrical resistance between the base plate and the metal plate.

The present invention has been achieved to solve the above problems, and an object of the present invention is to provide a power semiconductor device having an enhanced effect of suppressing radiation noise from a power semiconductor element and malfunction.

Solution to Problem

There is provided a power semiconductor device comprising: a mold unit that includes a power semiconductor element, a base plate, and a mold resin, the power semiconductor element being mounted on one surface of the base plate, a convex portion being formed on an other surface of the base plate, the convex portion including a plurality of grooves, the power semiconductor element being sealed with the mold resin in such a manner as to expose the convex portion; a plurality of radiation fins inserted into the grooves, respectively, and fixedly attached to the base plate by swaging; and a metal plate that includes a cut-off portion into which the convex portion is inserted, the metal plate being arranged between the mold unit and the radiation fins with the convex portion inserted into the cut-off portion, wherein the metal plate includes a protrusion that protrudes from an edge of the cut-off portion and that digs into a side surface of the convex portion when the convex portion is inserted into the cut-off portion.

Advantageous Effects of Invention

The power semiconductor device according to the present invention can reduce the electrical resistance between a base plate and a metal plate and enhance the effect of suppressing radiation noise from power semiconductor elements and malfunction.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of a power semiconductor device according to the present invention will be explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments.

First Embodiment

FIG. 1is an exploded perspective view of a configuration of a power semiconductor device according to a first embodiment of the present invention.FIG. 2is a cross-sectional view of the power semiconductor device according to the first embodiment. A power semiconductor device100according to the first embodiment includes a mold unit1, radiation fins2, and a metal plate3.

FIG. 3is a cross-sectional view of the mold unit in the power semiconductor device according to the first embodiment. The mold unit1includes power semiconductor elements11, a base plate12having one surface on which the power semiconductor elements11are mounted, and a mold resin13with which the power semiconductor elements11are sealed. The mold unit1is formed by integrally molding the base plate12on which the power semiconductor elements11are mounted with the mold resin13. A convex portion121is formed on a surface of the base plate12opposite to the surface on which the power semiconductor elements11are mounted, and the convex portion121protrudes from the mold resin13. A plurality of grooves122are provided in the convex portion121. Peripheral edges of the convex portion121form a flat surface123. The base plate12is formed using, as a material, a metal (such as aluminum) softer and higher in thermal conductivity than the metal plate3.

FIG. 4is a plan view of the metal plate in the power semiconductor device according to the first embodiment. A substantially rectangular opening31is cut off from the metal plate3as a cut-off portion, and the convex portion121can be inserted into the opening31. The substantially rectangular shape mentioned in this case includes a shape having rounded shape portion to prevent concentration of a stress on the corners. Protrusions32are provided on edges of two opposed sides (two short sides in this case) of the opening31. The distance L2between tip ends of the two protrusions32is smaller than the width L1of the convex portion121on the base plate12. The metal plate3is formed using a metal harder than the material of the base plate12. For example, a steel plate can be applied as the metal plate3.

The radiation fins2are thin-plate fins and as many radiation fins2as the grooves122provided in the convex portion121are prepared. The radiation fins2are inserted into the respective grooves122of the convex portion121, swaged in such a manner as to be pressed from left and right sides, and fixed to the base plate12.

FIGS. 5 and 6are enlarged cross-sectional views of a portion in which the metal plate contacts the base plate.FIG. 5depicts a state before the convex portion121is inserted into the opening31andFIG. 6depicts a state after the convex portion121is inserted into the opening31. Because the distance L2between the tip ends of the protrusions32is smaller than the width L1of the convex portion121on the base plate12, the protrusions32scrapes side surfaces124of the convex portion121when the convex portion121on the base plate12is inserted into the opening31, and the convex portion121is fitted into the opening31in a state in which the protrusions32dig into the side surfaces124of the convex portion121. At that time, an oxide film on the surface of the base plate12is damaged, an internal non-oxidized metal is exposed, and electrical connection between the metal plate3and the base plate12is realized. By allowing the protrusions32to act as portions in which the metals contact each other as a whole, an electrical resistance between the metal plate3and the base plate12can be reduced.

If the protrusions32are too small, it is difficult to secure a sufficient area of the portions made conductive as a result of the contact of the metals between the metal plate3and the base plate12. If the protrusions32are too large, a gap between the metal plate3and the base plate12becomes large to hinder the downscaling of the power semiconductor device100. When the size of each protrusion32is set to about 0.5 millimeter to 1.5 millimeters, it is possible to secure the area of the portions made conductive as a result of the contact of the metals between the metal plate3and the base plate12without increasing the power semiconductor device100in the size. However, this range is given only as an example and the present invention is not limited to this range.

The metal plate3of a shape having the protrusions32on the edges of only the two short sides of the opening31has been described by way of example. Alternatively, the protrusions32can be provided on edges of only long sides of the opening31or provided on the edges of both the short sides and the long sides thereof. When the protrusions32are provided on the edge of only one of two opposed sides of the opening31, a side surface of the metal plate3on the side on which no protrusions32are provided is pressed against the side surface124of the convex portion121. This can reduce the electrical resistance between the metal plate3and the base plate12as compared with a conventional structure that provides conduction on the flat surface123. Furthermore, the number of protrusions32provided on the edge of each side of the opening31is not limited to two but can be two or more, or two or less. Further, the number of protrusions32can be set differently among the edges of the respective sides of the opening31.

It has been described above that the opening31into which the convex portion121is inserted is cut off from the metal plate3as the cut-off portion. Alternatively, a notch33instead of the opening31can be cut off as the cut-off portion to form the metal plate3into a substantially U-shape.FIG. 7is an example of the metal plate from which the notch is cut off as the cut-off portion. When the notch33into which the convex portion121is inserted is cut off as the cut-off portion, the protrusions32can be formed on two opposed sides across an open side, thereby scraping the side surfaces124of the convex portion121when the convex portion121is inserted into the notch33. By providing the cut-off portion into which the convex portion121can be inserted to have a notch shape, it is possible to reduce an amount of the material used for the metal plate3.

The power semiconductor device according to the first embodiment can reduce the electrical resistance between the base plate and the metal plate and enhance the effect of suppressing radiation noise from the power semiconductor elements and malfunction.

Second Embodiment

A power semiconductor device according to a second embodiment is similar to that according to the first embodiment and includes the mold unit1, the radiation fins2, and the metal plate3as shown inFIGS. 1 and 2. As shown inFIG. 3, the mold unit1includes the power semiconductor elements11, the base plate12on which the power semiconductor elements11are mounted, and the mold resin13with which the power semiconductor elements11are sealed.FIG. 8is a plan view of the metal plate in the power semiconductor device according to the second embodiment. The opening31is cut off from the metal plate3as the cut-off portion and the convex portion121can be inserted into the opening31. A metal foil34is bonded to edges of four sides of the opening31. As the metal foil34, a foil such as a copper foil or an aluminum foil high in malleability and made of a softer metal than the metal plate3is applicable.

FIGS. 9 and 10are enlarged cross-sectional views of a portion in which the metal plate contacts the base plate.FIG. 9depicts a state before the convex portion121is inserted into the opening31andFIG. 10depicts a state after the convex portion121is inserted into the opening31. When the convex portion121on the base plate12is inserted into the opening31, the metal foil34deforms to conform to a shape of the gap between the base plate12and the metal plate3. By causing the metal foil34to fill the gap between the base plate12and the metal plate3, it is possible to increase a contact area in which the metal plate3contacts the base plate12and to reduce the electrical resistance between the metal plate3and the base plate12.

If the metal foil34is too thin, the metal foil34cannot sufficiently fill the gap between the base plate12and the metal plate3, and it is difficult to secure a sufficient contact area in which the metal plate3contacts the base plate12. If the metal foil34is too thick, the metal foil34does not easily deform, and it is difficult to secure a sufficient contact area in which the metal plate3contacts the base plate12. When the thickness of the metal foil34is set to about 0.1 millimeter to 0.3 millimeter, the contact area in which the metal plate3contacts the base plate12can be easily secured. However, this range is given only as an example and the present invention is not limited to this range.

It has been described above that the power semiconductor device is configured to use the metal plate3having the metal foil34bonded to the edges of the four sides of the opening31by way of example. It suffices to bond the metal foil34to the edge of at least one side of the opening31. However, it is desirable to arrange the metal foil34on the edges of all the sides of the opening31in view of increasing the contact area in which the base plate12contacts the metal plate3. Similarly to the first embodiment, the notch33instead of the opening31can be cut off from the metal plate3as the cut-off portion.

Similarly to the first embodiment, the power semiconductor device according to the second embodiment can reduce the electrical resistance between the base plate and the metal plate and enhance the effect of suppressing radiation noise from the power semiconductor elements and malfunction.

INDUSTRIAL APPLICABILITY

As described above, the power semiconductor device according to the present invention is useful in a feature that it can enhance the effect of suppressing radiation noise from power semiconductor elements and malfunction.

REFERENCE SIGNS LIST