Semiconductor switching device

The invention relates to a semi-fabricated switching device comprising a semiconductor element and a housing comprising a spring system with a ring-shaped washer laterally surrounding the semiconductor element for clamping the semiconductor element between two pole pieces. The washer is deflectable between the pole pieces by a first deflection element, which contacts the washer in a first contact area on a first side, and by a second deflection element, which contacts the washer in a second contact area on a second side. The first contact area is displaced to the second contact area. The first and second deflection element can deflect the washer such that in clamped condition an electrical contact is achievable between the pole pieces and the semiconductor element.

FIELD OF THE INVENTION

The invention relates to the field of power electronics, in particular to a semiconductor switching device.

BACKGROUND OF THE INVENTION

Semiconductor switching devices are powerful and fast turnoff components having a cathode-anode-gate structure. Specifically, the semiconductor switching device comprises a semiconductor element having deposited thereon a cathode, an anode, and a gate of the switching device. The device further comprises connection means for electrically connecting the cathode, the anode and the gate of the switching device to an external circuit unit.

A semiconductor element has to handle large currents and voltages. One example of such a semiconductor element is an integrated gate commutated thyristor (IGCT). An IGCT is a gate-controlled turn-off switch which turns off like an insulated gate bipolar transistor (IGBT), but conducts like a thyristor with the lowest conductor losses. An integrated gate commutated thyristor is a power switching device for demanding high power applications such as, e.g. medium voltage drives, traction, wind power converters, AC excitation systems, battery energy storage systems, solid state breakers, traction line boosters, traction power compensators and induction heating.

A semiconductor element constructed as an IGCT nowadays is used in a variety of applications due to its versatility, efficiency and cost effectiveness. A conventional IGCT device has a ring-shaped structure where on a cathode disc a gate disc is arranged providing a gate connection to the switching device. An anode phase is arranged on top of a housing having for instance a specific creepage distance at the outside.

US 2016071815 A1 shows a semiconductor switching device having a semiconductor element1and a housing with a spring system, by which the semiconductor element1is clamped between the cathode and anode pole piece3,4(FIG. 1). The spring system comprises two Belleville springs69,69′, which are clamped between the pole pieces3,4and thereby clamp the semiconductor element1to achieve a contact of the main electrodes of the semiconductor element to the pole pieces3,4. An insulating ring9with an L profile is arranged between the semiconductor element1and the spring system. One of the Belleville springs69′ lies on the insulating ring9with gate leads clamped in between. Additional support elements68,68′ are positioned between the Belleville springs and the insulating ring9to protect the insulating ring9and gate leads from sharp edges of the Belleville spring69,69′.

Such a semiconductor switching device may be semi-fabricated with the semiconductor element1positioned between the pole pieces3,4and the spring system surrounding the semiconductor element1. The semi-fabricated switching device can be shipped from a factory to a costumers' place, where it can be can be installed in its final surrounding and clamped to establish the electrical contact from the semiconductor element1to the pole pieces3,4.

For manufacturing the semi-fabricated semiconductor switching device it is important to be able to mount the semiconductor element easily in the housing. Furthermore, proper alignment and support of all parts inside a housing is important to guarantee proper contacting even after transport.

EP 1 220 314 A2 shows another prior art pressure contact for a thyristor module. Two ring pieces surrounding the thyristor latch in each other by having protrusions and recesses. To the lateral sides, the ring system is insulated by an insulation element. On the top side, an electrical main connector leads upwards. Each thyristor element is fixed to the base plate by three tension screws arranged around each ring system. To the bottom side, a plurality of such thyristors are separately insulated from a base plate. The thyristors are arranged laterally from each, electrically connected to each other by a common main electrode plate, i.e. no compact arrangement is possible and the thyristors cannot be arranged in stack configuration. As all thyristors have to be directly mounted on the common base plate together, no modular design and no semi-fabrication is possible. The applied spring force depends on the force, by which each tension screw is tightened. Furthermore, as a plurality of tension screws have to be tightened for each semiconductor element, a tilting is possible, which may lead to bad or no electrical connection from the semiconductor element to the pole pieces.

DE 29 42 585 describes a semiconductor device, in which a semiconductor element is clamped between cathode and anode pole pieces with a deflectable silicon ring between the pole pieces. Outwardly arranged extensions of the pole pieces are pressed together by an insulator with inwardly tapered extensions, which cover the extensions of the pole pieces. The silicon ring is pressed against the pole pieces along a circular area on opposite sides of the silicon ring.

DESCRIPTION OF THE INVENTION

It is an objective of the invention to provide a semi-fabricated switching device and a semiconductor switching device as such with a spring system, which is easy to mount, cost efficient and reliable.

An inventive semi-fabricated semiconductor switching device comprises a semiconductor element having a cathode side and an anode side opposite to the cathode side and a housing. The housing comprises a cathode pole piece, which is arranged on the semiconductor element on the cathode side, an anode pole piece, which is arranged on the semiconductor element on the anode side, wherein the cathode pole piece and the anode pole piece laterally project beyond the semiconductor element. A spring system laterally surrounds the semiconductor element for clamping the semiconductor element between the cathode pole piece and anode pole piece.

The spring system comprises a ring-shaped washer laterally surrounding the semiconductor element, which washer has a first side and second side opposite to the first side. The washer is made of a material, which keeps its shape reproducibly under deformation at least up to a spring deflection. The washer is deflectable between the cathode pole piece and the anode pole piece by a first deflection element, which contacts the washer in a first contact area of the washer on the first side, and by a second deflection element, which contacts the washer in a second contact area of the washer on the second side, wherein the first contact area is displaced to the second contact area. The first deflection element and the second deflection element are adapted to deflect the washer during clamping by a strain distance, which is less or equal to the spring deflection, wherein the strain distance is so large that in clamped condition an electrical contact is achievable between the cathode pole piece, the semiconductor element and the anode pole piece.

The washer in form of a spring washer is a very simple and low cost element. As large force, exemplarily of at least 1 kN is applied on the pole pieces, and as the strain distance is small, exemplarily up to 1.5 mm, there are no high requirements for the spring properties of the washer. Therefore, no sophisticated spring system is needed. The deflection elements define the maximum strain distance and equalize the height differences between the washer and the pole pieces, the washer itself does not have high height requirements so that the same washer may be used for different switching devices.

The deflection elements are simple and low costs elements, which may be have protrusions as rings, pins or bars. The deflection elements may also be integrally formed with the pole pieces, a gate lead ring or an insulation ring. Such an integrally formed deflection element does not have to be separately mounted and therefore, makes the manufacturing simpler. A combination of one integrally formed deflection element (with the pole piece, insulation ring or gate leads) and one separate deflection element combines the advantages of simple mounting and modular constructions.

Alignment elements on the deflection elements and/or on the washer can help to mount the elements in correct position.

The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of designations. In principle, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows a semi-fabricated semiconductor switching device comprising a semiconductor element1such as an IGCT having a cathode side10and an anode side12opposite to the cathode side10and a housing2. In an exemplary embodiment, the semiconductor element1is an IGBT. The housing2comprises a cathode pole piece3, which is arranged on the semiconductor element1on the cathode side10, an anode pole piece4, which is arranged on the semiconductor element1on the anode side12, wherein the cathode pole piece3and the anode pole piece4laterally project the semiconductor element1, and a spring system laterally surrounding the semiconductor element1for clamping the semiconductor element1between the cathode pole piece3and anode pole piece4. The spring system is deflectable, i.e. compressible by clamping the pole pieces3,4of the semiconductor switching device together. A semi-fabricated switching device shall mean that the semiconductor element1is assembled between a cathode pole piece3and an anode pole piece4with a spring system prepared for clamping the semiconductor element1between the cathode and anode pole piece3,4.

The spring system comprises a ring-shaped washer6laterally surrounding the semiconductor element1, which washer6has a first side60and second side62opposite to the first side60, a first deflection element7and a second deflection element8. The washer6is made of a material, which keeps its shape reproducibly under deformation at least up to a spring deflection. The washer may be made of steel. Exemplarily, the washer6is made of spring steel, which is exemplarily a carbon comprising steel with a very high yield strength. Such material allows objects made of spring steel to return to their original shape despite deflection within the spring deflection, which is the maximum distance, by which the spring can be deflected without irreversibly deforming the spring.

The washer6is a hollow cylinder (ring) having a cylinder height and a width (which is the difference between an outer radius or an outer edge66and an inner radius or an inner edge65of the cylinder). The washer6is deflectable between the cathode pole piece3and the anode pole piece4by a first deflection element7, which contacts the washer6in a first contact area61of the washer6on the first side60, and by a second deflection element8, which contacts the washer6in a second contact area63of the washer6on the second side62. The first contact area61is displaced to the second contact area63so that the washer is deflectable between the first and second contact area61,63by the first deflection element7and the second deflection element8, through which a force can be exerted on the washer6. The first deflection element7and the second deflection element8are adapted to deflect the washer6during clamping by a strain distance64such that the first deflection element7and the second deflection element8can deflect the washer6by a strain distance64. The first deflection element7comprises at least one protruding element and the second deflection element8comprises at least one protruding element, at which protruding elements the deflection elements7,8contact the washer6. As the protruding elements of the first and second deflection element7,8are positioned displaced and act on opposite sides of the washer6, the washer6can be deflected by the deflection elements7,8being pressed towards each other. The protruding elements of the first and second deflection elements7,8are displaced at least by a distance, which corresponds to the height of the washer6, so that the washer can be, i.e. is adapted to be strained between the two deflection elements7,8up to a strain distance64, which is less or equal to the spring deflection. The spring deflection shall be the maximum deflection distance, by which the spring (i.e. the washer6) can be deflected, and at which the washer6returns to its original shape after releasing any applied force. The strain distance64is so large that in clamped condition an electrical contact is achievable between the cathode pole piece3, the semiconductor element1and the anode pole piece4, i.e. in a clamped condition the semiconductor element1contacts the cathode pole piece3on the cathode side10and the anode pole piece4on the anode side12.

InFIG. 1the strain distance64is shown as the distances64_1and64_2to indicate the cathode pole piece3and the anode pole piece4have to be brought into contact with the semiconductor element1. The distance64_1and64_2corresponds to the strain distance64, by which the washer6has to be deflected.

In an exemplary embodiment, the semi-fabricated device comprises two strain buffer plates5,5′, one of which is arranged between the semiconductor element1and the cathode pole piece3and one of which is arranged between the semiconductor element1and the anode pole piece4(FIG. 2). The strain buffer plates5,5′ are made of an electrically conductive material, which has a coefficient of thermal expansion which is between that of the semiconductor element and said pole piece, which is in contact to the strain buffer plate5,5′, exemplarily the strain buffer plates5,5′ are made of Molybdenum. As the strain buffer plates5,5′ are arranged between the pole pieces3,4and the semiconductor element1, they have to be clamped between the pole pieces3,4and the semiconductor element1to establish the electrical contact.

In an exemplary embodiment shown inFIG. 5the first deflection element7is ring-shaped with a plurality of first protruding elements70,70′,70″,70′″ each having a first height72or at least the first height72. The height of a protruding element shall be such height, by which the protruding element projects an area in between two protruding elements (at which area the protruding element of the other/opposite lying deflection element acts/contacts on the washer). The first protruding elements70,70′,70″,70′″ are spaced from each other along a first ring abutting surface73towards the first side60of the washer6. The second deflection element8has a plurality of second protruding elements80,80′,80″,80′″ each having a second height82or at least the second height82. The second protruding elements80,80′,80″,80′″ are spaced from each other along a second ring abutting surface83towards the second side62of the washer6. The first protruding elements70,70′,70″,70′″ contact the washer6at the first contact area61and the second protruding elements80,80′,80″,80′″ contact the washer6at the second contact area63. The first protruding elements70,70′,70″,70′″ are positioned laterally to and in a displaced manner to the second protruding elements80,80′,80″,80′″, so that the first protruding elements70,70′,70″,70′″ deflect the washer6in a first area61displaced from the second contact area63, at which the second protruding elements80,80′,80″,80′″ contact the washer6. Displaced shall mean that the elements are arranged lateral to each other in a plane parallel to the cathode side10. The first height72as well as the second height82is at least as large as the strain distance64. The washer6can be deflected between the first and second deflection elements7,8such that the deflected washer has a wave shape along its circular direction. In such an arrangement, such sides of the deflection elements7,8, on which the first protruding elements70,70′,70″,70′″ and the second protruding elements80,80′,80″,80′″ are arranged, face each other. The first protruding elements70,70′,70″,70′″ and/or the second protruding elements80,80′,80″,80′″ may be arranged in a regular distance to each other, i.e. the first protruding elements70,70′,70″,70′″ may be arranged equidistant from each other and/or the second protruding elements80,80′,80″,80′″ may be arranged equidistant from each other.FIG. 5shows such a first and second deflection element7,8with a washer6to be placed between the deflection elements7,8.

FIG. 6shows a cut through an inventive semiconductor switching device, in which a first protruding element70deflects the washer6towards the anode pole piece4. Depending on the strain distance64and the first height72the washer6may touch the second deflection element8(in an area having no second protrusion element), but there may also be a distance between washer6and the second deflection element8.FIG. 7shows a cut through the same inventive semiconductor switching device as inFIG. 6, but at another place of the washer ring6, in which a second protruding element80deflects the washer6towards the cathode pole piece3. Depending on the strain distance64and the second height82the washer6may touch the first deflection element7(in an area having no first protrusion element), but there may also be a distance between washer6and the first deflection element7.

In an exemplary embodiment shown inFIGS. 8 and 9, the first and/or second deflection element7,8is formed such that in such areas, in which a first protruding element70,70′,70″,70′″, no second deflection element is arranged on the other side of the washer and/or vice versa. Depending on the strain distance64and the first height72the washer6may touch the anode pole piece4(FIG. 8), but there may also be a distance between washer6and the anode pole piece4. Correspondingly, depending on the strain distance64and the second height82the washer6may touch the cathode pole piece3(in an area having no first protrusion element), but there may also be a distance between washer6and the cathode pole piece3. Such design may be achieved by the first and/or second protruding elements70,70′,70″,70′″,80,80′,80″,80′″ being integrally formed with another element of the switching device, i.e. one of the pole pieces3,4, the gate leads or the insulating ring9. Alternatively, the protruding elements70,70′,70″,70′″,80,80′,80″,80′″ may be formed with a ring laterally surrounding the protruding elements, so that no deflection element is between the washer6and the pole pieces at such areas, in which no protruding element is arranged.

In an exemplary embodiment, at least one or all first protruding element70,70′,70″,70′″ is/are arranged at a central position between two second protruding elements80,80′,80″,80′″. Also at least one or all second protruding element80,80′,80″,80″ is/are arranged at a central position between two first protruding elements70,70′,70″,70′″.

In an exemplary embodiment, the first deflection element7is made of an electrically conductive material and it contacts a semiconductor gate electrode of the semiconductor element1. The gate electrode may be electrically connected to an external circuit unit via the first protruding elements70,70′,70″,70″. The first protruding elements70,70′,70″,70′″ are arranged around the semiconductor element1(FIG. 10). In this embodiment, the first protruding, electrically conductive elements70,70′,70″,70′″ act additionally to their function as deflection element as gate leads, i.e. the first deflection element7forms a gate lead ring.

TheFIGS. 14 to 17show an exemplary embodiment of an inventive device, in which the washer6is deflected on one side by gate leads, which act as first protruding elements70,70′,70″,70′″ and a second deflection element8having second protruding elements80,80′. On a lateral side, the semiconductor element is insulated by an insulator90. TheFIGS. 14 and 16show the device in unclamped condition, theFIGS. 15 and 17in clamped condition. Two first protruding elements70,70′ and70″,70′″ are arranged between two second protruding elements80,80′. The dashed part of the first deflection element shall indicate that the first deflection element7leads out of the device for electrically contacting the gate electrode.

In an exemplary embodiment, an insulating ring9may laterally surround the semiconductor element1. The ring is positioned between the semiconductor element1and the washer6(FIG. 4).

In an exemplary embodiment, the second deflection element8is made of an insulating material. In this embodiment, the second deflection element8may also separate the semiconductor element1from the washer6, i.e. the second deflection element8may be integrally formed with the insulating ring9such that the second deflection element8separates the semiconductor element1from the washer6.

The number of first protruding elements70,70′,70″,70′″ may differ from the number of second protruding elements80,80′,80″,80′″, so that two first or second protruding elements70,70′,70″,70′″ or80,80′,80″,80′″ may be neighboured without a second or first protruding element80,80′,80″,80″ or70,70′,70″,70″ in between. This can have advantages, e.g. if the first protruding elements70,70′,70″,70″ are gate leads, so that the number of gate leads can be optimized for the gate current flow independently from the number of first protruding elements70,70′,70″,70′″ as deflection means. Exemplarily, additionally to gate leads, further first protruding elements could be added of insulating material.

In an exemplary embodiment, the first deflection element7has a ring-shaped third protruding element75having a third height76, which contacts the washer6at the first contact area61along an inner edge65of the washer (FIG. 11). The figure shows a vertical cut through the semi-fabricated device. The second deflection element8also has a ring-shaped fourth protruding element85having a fourth height86, which contacts the washer6at the second contact area63along an outer edge66of the washer6. The third height76and the fourth height86is at least as large as the strain distance64. The third and fourth protruding elements75,85face each other. As one of the protruding elements contacts the washer6at the inner edge65and the other protruding element contacts the washer6at the outer edge66, the first and second protruding elements75,85are displaced to each other.FIG. 12shows the first and second deflection elements7,8ofFIG. 11in clamped condition. The third and fourth protruding elements75,85have a distance to each other in clamped condition, which is at least as large as the thickness of the washer6, so that the washer can be clamped between the third and fourth protruding elements75,85. Exemplarily, the third and fourth protruding elements75,85are ring-shaped having a width, which is less than 25% of a width of the washer6. The first and/or second deflection elements7,8may be discrete ring-shaped elements (formed as a ring, exemplarily with an L-profile or a pure hollow cylinder). In another alternative embodiment, the third and/or fourth protruding elements75,85, and thus, the first and/or second deflection elements7,8is or are integrally formed with the cathode and/or anode pole piece4or the insulating ring9. Exemplarily, one of the pole pieces3,4has a rim (ring-shaped protruding element at the side towards the washer6, at which the washer6can rest) or the insulating ring9has a L-shape, at which the washer6can rest at the first contact area61. In this embodiment, the washer6is deflected along its width direction.

In an exemplary embodiment, the first deflection element7is ring-shaped with a plurality of first protruding elements70,70′,70″,70′″ each having a first height72. The first protruding elements70,70′,70″,70′″ are spaced from each other along a ring abutting surface73. The first deflection element7further comprises a ring-shaped third protruding element75having a third height76, which contacts the washer6along an inner edge65of the washer. The second deflection element8is also ring-shaped with a plurality of second protruding elements80,80′,80″,80′″ each having a second height82. The second protruding elements80,80′,80″,80′″ are spaced from each other along a ring abutting surface83. The second deflection element8further comprises a ring-shaped fourth protruding element85having a fourth height86, which contacts the washer6along an outer edge66of the washer. The first protruding elements70,70′,70″,70′″ are positioned in a displaced manner to the second protruding elements80,80′,80″,80′″. The first protruding elements70,70′,70″,70′″ and the third protruding element75face the second protruding elements80,80′,80″,80′″ and the fourth protruding element85. At least one of or both of a) the first height72and the second height82is at least as large as the strain distance64and b) the third height76and the fourth height86is at least as large as the strain distance64. In this embodiment, the washer6is deflected in its width direction (i.e. between the inner and outer edge65,66) as well as along its circular direction (ring abutting surface).

In an exemplary embodiment, the invention concerns a semiconductor switching device, in which a semiconductor element1is clamped between the cathode pole piece3and the anode pole piece4such that the cathode pole piece3, the semiconductor element1and the anode pole piece4are electrically connected. In this embodiment, the first deflection element7and the second deflection element8deflect the washer6by the strain distance64. A clamping element20clamps the semiconductor element1between the cathode and anode pole piece3,4(FIGS. 3 and 4; the figures do not show any details of the washer, in particular these figures do not indicated the shifted positions of the first or second contact area). The spring system laterally from and surrounding the semiconductor element1allows to achieve a reliable electrical connection between the pole pieces3,4and the semiconductor element1. Exemplarily, a force is applied on the pole pieces3,4by the clamping element20, due to which the first deflection element7and the second deflection element8deflect the washer6with a spring force of at least 1 kN. The strain distance64, by which the washer6is compressed, is exemplarily at least 0.2 mm. In another exemplary embodiment, the strain distance64is between 0.2 mm and 1.5 mm or between 0.4 and 0.6 mm. Such a spring force and such a distance ensure that the electrical connection between semiconductor element1and pole pieces3,4is reliable.

FIG. 4shows an exemplary embodiment, in which an insulating ring9is arranged between the semiconductor element1and the washer6, so that the semiconductor element1is separated from the spring system.

The deflection elements3,4may comprise an alignment element, by which the position of the protruding elements70,70′,70″,70′″,80,80′,80″,80′″ is defined. Such alignment elements may be pins and recesses or any other position fixation elements.

The housing2may comprises more elements well-known to the persons skilled in the art. Exemplarily, the housing comprises an insulation tube92having creepage sections at the outside thereof in order to deviate creepage currents (FIGS. 14 and 15).

LIST OF DESIGNATIONS