Holding and ignition prevention device for semiconductor element, and power conversion device using holding and ignition prevention device

A problem to be solved by the present invention is to prevent smoke emission and ignition of a power semiconductor element that is installed inside a power conversion device connected to a battery in the field of power electronics, for example. A semiconductor holding device according to the present invention includes: a package which houses a power semiconductor element therein and dissipates heat to a cooler from a first surface of the package; a plate covering a second surface opposing the first surface of the package; and a pressing member pressing the plate against the package.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2016/076762 filed Sep. 12, 2016.

TECHNICAL FIELD

The present invention relates to a semiconductor element holding device that is installed inside a power conversion device connected to a battery, and a power conversion device using the holding device, in the field of power electronics.

BACKGROUND ART

In a conventional semiconductor element holding structure, a spring support member including a leaf spring portion and a supporting portion brings the leaf spring portion into abutment against an upper surface of a semiconductor element, thus fixing the semiconductor element to the heat dissipation plate side with a predetermined elastic force (see, e.g., Patent Document 1). In general, it is often the case that the power semiconductor element provided inside a vehicle-mounted power conversion device is fixed in the same manner as that described above.

CITATION LIST

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In the vehicle-mounted power conversion device disclosed in Patent Document 1, the vehicle-mounted power conversion device is connected to a lead battery on the vehicle side. Accordingly, if a short circuit failure occurs in a rectification diode, a large current flows in from the lead battery, resulting in smoke emission and ignition.

An object of the present invention is to provide a countermeasure with a simple structure, against smoke emission and ignition that are caused by a short circuit failure of the power semiconductor element mounted inside the power conversion device.

Solution to the Problems

A semiconductor element holding device according to the present invention includes: a package which houses a power semiconductor element therein and dissipates heat to a cooler from a first surface of the package; a plate covering a second surface opposing the first surface of the package; and a pressing member pressing the plate against the package.

Effect of the Invention

According to the present invention, the package housing the power semiconductor element therein is pressed by the plate, so that oxygen will not flow in from cracks caused in the package in the event of a short circuit failure of the power semiconductor element, thus making it possible to prevent smoke emission and ignition of the power semiconductor element.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of a semiconductor element holding structure according to the present invention will be described with reference to the drawings. In the following description, identical or equivalent elements are denoted by identical reference numerals.

FIG. 1is a circuit configuration diagram illustrating a DC-DC converter serving as a power conversion device according to Embodiment 1 of the present invention.

The secondary side of the transformer of this circuit employs a center tap-type diode rectification scheme, and can obtain a rectified waveform equivalent to that obtained by a full-wave rectification circuit. InFIG. 1, a voltage higher than the output voltage of an output terminal111is applied to input terminals101aand101bto which a DC voltage is applied. The DC voltage that has been inputted into the input terminals101aand101bis converted into an AC voltage by an inverter circuit102. In general, the inverter circuit102is constituted by a switching element such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Field-Effect Transistor).

The AC voltage that has been outputted from the inverter circuit102is applied to a transformer primary winding103. An AC voltage that is similar to a rectangular wave and generated by switching the semiconductor element provided in the inverter circuit102in accordance with a driving signal supplied from a driving circuit (not shown) is applied to the transformer primary winding103.

The secondary side of the transformer includes a transformer upper secondary winding104and a transformer lower secondary winding105to which an AC voltage converted into a varied voltage level depending on the turns ratio of the transformer is applied.

The transformer primary winding103, the transformer upper secondary winding104, and the transformer lower secondary winding105are electromagnetically coupled by a magnetic substance core106. The windings constituting the transformer are disposed around a middle leg provided on the magnetic substance core106.

Rectification elements107aand107bare each constituted by a power semiconductor element, and rectify the AC voltage outputted from the transformer upper secondary winding104and the transformer lower secondary winding105. A ripple voltage waveform rectified by the rectification elements107aand107bis smoothed by a smoothing circuit including a reactor109and a capacitor110, and the DC voltage obtained by the smoothing circuit is outputted from the output terminal111. In the present embodiment, a ground terminal108of the secondary-side circuit is set at the same potential as the metal casing, and therefore the output voltage is outputted between the output terminal111and the metal casing.

In the DC-DC converter configured in this manner, the DC input voltage supplied from the input terminals101aand101bundergoes switching by the inverter circuit102so as to generate an input AC voltage, and the input AC voltage is supplied to the transformer primary winding103. Then, the generated input AC voltage is transformed, and is outputted as an output AC voltage from the transformer upper secondary winding104and the transformer lower secondary winding105. Then, the output AC voltage is rectified by the rectification elements107aand107b, and is also smoothed by the smoothing circuit including the reactor109and the capacitor110, and a DC voltage is supplied from the output terminal111to a lead battery112provided on the vehicle.

However, if a short circuit failure occurs in the rectification element107b, a large current flows into the rectification element107bfrom the lead battery112as indicated by an arrow113, and the rectification element107bmay cause smoke emission and ignition. That is, in the case where a very thin aluminum wire is used to provide connection inside the rectification element107b, the aluminum wire is melted earlier than a quick-blown fuse provided on the vehicle side, so that the epoxy resin around the aluminum wire is carbonized, thus forming an electric conduction path from the lead battery112. In addition, the large current causes cracks in the epoxy resin, and oxygen is supplied from the cracked locations, thus causing smoke emission and ignition.

A semiconductor element holding structure that prevents a supply of oxygen caused by cracks in the epoxy resin described above is shown inFIG. 2. Although a description will be given of the rectification elements107aand107bshown inFIG. 1as an example of the semiconductor element, the holding structure can be used not only for the rectification element, but also for a power semiconductor element in which the same problem occurs.

FIG. 2is an assembly perspective view showing a holding structure200for a rectification element package201housing therein the rectification element107aor107bshown inFIG. 1.

In the rectification element package201, recesses202aand202bthat are each cut out into a semicircular shape are formed on both sides of an upper portion on a side opposite to the side from which terminals of the rectification element are exposed, and a package hole portion203for passing a fixing screw209therethrough is provided between the recesses202aand202b.

A plate204having an area one size larger than the area of an upper surface of the rectification element package201is disposed in contact with the upper surface. The plate204is made of a material such as metal or resin, and plate protrusions205aand205bthat are bent perpendicularly from the upper surface of the plate toward the rectification element package201are formed at both side portions that correspond to the recesses202aand202bof the rectification element package201. The plate protrusions205aand205bare engaged with arc-shaped side surfaces of the recesses202aand202bso as to position the rectification element package201and the plate204relative to each other. Also in the plate204, a plate hole portion206is provided at the same position as the package hole portion203.

A heat dissipation sheet207is disposed in contact with a lower surface of the rectification element package201. A heat dissipation sheet hole portion208through which the fixing screw209passes is also formed in the heat dissipation sheet207. Also, a heat spreader (not shown) made of a metal is disposed on the lower surface of the rectification element package201.

The fixing screw209passes through the plate hole portion206, the package hole portion203, and the heat dissipation sheet hole portion208, and is screwed with a screw groove of a cooler hole portion210provided in a cooler (not shown). Consequently, the plate204, the rectification element package201, and the heat dissipation sheet207are fixed together, and are mechanically fixed to the cooler.

Since the plate204is pressed against the upper surface of the rectification element package201by such a holding structure200, it is possible to block any oxygen from flowing due to occurrence of cracks in the rectification element package201when the rectification element undergoes a short circuit failure. Since the area of the plate204is configured to be larger than the area of the rectification element package201, the upper surface of the rectification element package201can be reliably covered by the plate204. In addition, as a result of the recesses202aand202bbeing engaged with the plate protrusions205aand205b, it is possible to prevent positional displacement and rotation of the plate205during assembly. It is noted that the shapes of the recesses202aand202band the plate protrusions205aand205bare not limited to those shown inFIG. 2, and may be any shapes as long as they can prevent positional displacement and rotation.

In addition, the heat spreader is disposed on the lower surface of the rectification element package, thus providing a structure into which oxygen is difficult to flow. Furthermore, pressing against the cooler is performed by the fixing screw209. Accordingly, the cooler serves the same function as that of the plate204and prevents entry of oxygen.

Another embodiment of the semiconductor element holding structure will be described with reference toFIG. 3. Although a description will be given of the rectification elements107aand107bshown inFIG. 1as an example of the semiconductor element, the holding structure can be used not only for the rectification element, but also for a power semiconductor element in which the same problem occurs, as in Embodiment 1.

FIG. 3is an assembly perspective view showing a holding structure300for a rectification element package301housing therein the rectification element107aor107bshown inFIG. 1.

A plate302having an area one size larger than the area of an upper surface of the rectification element package301is disposed in contact with the upper surface. The plate302is made of a material such as metal or resin, and outer peripheral surfaces302a,302b, and302cthat are bent perpendicularly from the upper surface of the plate toward the rectification element package301are formed on the outer peripheral portion of the plate302. The outer peripheral surfaces302a,302b, and302care engaged with the respective corresponding side portions of the rectification element package301. A heat dissipation sheet303is disposed in contact with a lower surface of the rectification element package301. One end portion304aof a spring member304is in contact with the upper surface of the plate302, a fixing screw306passes through a spring member hole portion305which is formed in the other end portion304band through which the fixing screw passes, and thus the fixing screw306is screwed with a screw groove of a cooler hole portion307provided in a cooler. Consequently, the spring member304is mechanically fixed to the cooler, and also presses the plate302, the rectification element package301, and the heat dissipation sheet303against the cooler.

Since the plate302is pressed against the upper surface of the rectification element package301by such a holding structure300, it is possible to block any oxygen from flowing due to occurrence of cracks in the rectification element package301when the rectification element undergoes a short circuit failure. Since the area of the plate302is configured to be larger than the area of the rectification element package301, the upper surface of the rectification element package301can be reliably covered by the plate302. In addition, the plate302has the perpendicular outer peripheral surfaces302a,302b, and302calong the outer peripheral portion of the plate, and is mounted so as to hold the rectification element package301therein during assembly. Accordingly, it is possible to prevent positional displacement and rotation of the plate during assembly. It is noted that, as in Embodiment 1, a heat spreader (not shown) is disposed on the lower surface of the rectification element package301, thus providing a structure into which oxygen is difficult to flow. Furthermore, pressing against the cooler is performed by the spring member304. Accordingly, the cooler serves the same function as that of the plate302and prevents entry of oxygen.

Another embodiment of the semiconductor element holding structure will be described with reference toFIG. 4. Although a description will be given of the rectification elements107aand107bshown inFIG. 1as an example of the semiconductor element, the holding structure can be used not only for the rectification element, but also for a power semiconductor element in which the same problem occurs, as in Embodiments 1 and 2.

FIG. 4is an assembly perspective view showing a holding structure400for a plurality of rectification element packages401each housing therein the rectification element107aor107bshown inFIG. 1.

A single plate402capable of covering the plurality of rectification element packages401is disposed in contact with upper surfaces of the plurality of (in this drawing, four) rectification element packages401. The plate402is made of a material such as metal or resin, and outer peripheral surfaces402a,402b, and402cthat are bent perpendicularly from the upper surface of the plate toward the rectification element packages401are formed on the outer peripheral portion of the plate402. The outer peripheral surface402bis engaged with a side portion401bof each of the plurality of rectification element packages401, and the outer peripheral surfaces402aand402care respectively engaged with side portions401aand401clocated at end portions of the plurality of rectification element packages401. A heat dissipation sheet403is disposed in contact with lower surfaces of the rectification element packages401. One end portion404aof each of a plurality of (in this drawing, two) spring members404is in contact with the upper surface of the plate402, fixing screws406pass through spring member hole portions405aand405bwhich are formed in the other end portions404band through which the fixing screws pass, and thus the fixing screws406are screwed with screw grooves of cooler hole portions407aand407bprovided in the cooler. Consequently, the spring members404are mechanically fixed to the cooler, and also press the plate402, the rectification element package401, and the heat dissipation sheet403against the cooler.

Since the plate402is pressed against the upper surfaces of the plurality of rectification element packages401by such a holding structure400, it is possible to block any oxygen from flowing due to occurrence of cracks in each of the rectification element packages401when the rectification element undergoes a short circuit failure. Since the area of the plate402is configured to be larger than the total area of the plurality of rectification element packages401, the upper surfaces of the plurality of rectification element packages401can be reliably covered by the plate402. In addition, the plate402has the perpendicular outer peripheral surfaces402a,402b, and402calong the outer peripheral portion of the plate, and the single plate402is mounted so as to hold the plurality of rectification element packages401therein during assembly. Accordingly, it is possible to prevent positional displacement of the plate during assembly, and also to decrease the number of components, thus reducing the number of man-hours for assembly. As in Embodiments 1 and 2, a heat spreader (not shown) is disposed on the lower surfaces of the rectification element packages401, providing a structure into which oxygen is difficult to flow. Furthermore, pressing against the cooler is performed by the spring members404. Accordingly, the cooler serves the same function as that of the plate402and prevents entry of oxygen.

Recently, rectification elements, switching elements, and the like that use a wide bandgap semiconductor such as a SiC or GaN semiconductor as a semiconductor element, other than a Si semiconductor, have been increasingly used for an inverter circuit or the like. Such wide bandgap semiconductors are operated at a higher frequency than the Si semiconductor, and therefore, are generally considered to have higher failure probability, and thus are more likely to cause smoke emission and ignition. However, application of the present invention makes it possible to prevent smoke emission and ignition, and is suitable for a power semiconductor element using a wide bandgap semiconductor.

It is noted that, within the scope of the present invention, the above embodiments may be freely combined with each other, or each of the above embodiments may be modified or simplified as appropriate.

DESCRIPTION OF THE REFERENCE CHARACTERS