Power semiconductor arrangement

A power semiconductor device comprises a substrate; and power semiconductor components disposed on and connected thereto. The device includes a housing part with a housing wall having a first cutout. The device has, for making electrical contact therewith, a unitary load connection element which passes through the first cutout in an X direction, is electrically conductive, and has an outer connection section disposed outside the housing part and an inner connection section disposed within the housing part. A first bush which has an internal thread running in the X direction is rotationally fixed and movable in the X direction in the housing wall. The first outer connection section has a second cutout aligned with the first bush. The load connection element has a first holding element disposed near the first cutout, the holding element engaging in a groove in the housing wall which runs perpendicular to the X direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a power semiconductor device.

2. Description of the Related Art

In known power semiconductor devices, power semiconductor components, such as power semiconductor switches and diodes, are generally disposed on a substrate and electrically conductively connected to one another by a conductor layer of the substrate as well as bonding wires and/or a film composite. The power semiconductor switches in this case are generally in the form of transistors, such as, for example, IGBTs (Insulated-Gate Bipolar Transistors) or MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors) or in the form of thyristors.

The power semiconductor components disposed on the substrate are in this case often electrically interconnected to form one or more so-called half-bridge circuits, which are used, for example, for rectifying and inverting electric voltages and currents.

Conventional power semiconductor devices have load connection elements for conducting load currents, with the aid of which load connection elements the power semiconductor devices are electrically conductively connected to external components via electrically conductive power line elements, such as busbars, for example. The load currents in this case generally have a high current intensity in comparison with auxiliary currents which are used for actuating the power semiconductor switches, for example. The load connection elements generally run through the housing of the respective power semiconductor device. The load connection elements each have an outer connection section disposed outside the housing and an inner connection section disposed within the housing. The inner connection section of the load connection elements is intended to move as little as possible or to be subjected to compressive or tensile loading as little as possible when electrical contact is made (for example by screw connections) between the load connection elements and the power line elements, such as, for example, the busbars, and during operation of the power semiconductor device since, as a result, the life of the electrically conductive connections between the load connection elements and, for example, the substrate of the power semiconductor device, which connections are disposed in the interior of the housing of the power semiconductor device, is reduced. Owing to mechanical tolerances of the power line elements and the power semiconductor device and the spacing thereof from one another, compressive or tensile loading often occurs at the outer connection sections of the load connection elements, which results in the above-described undesired movements of the inner connection sections of the load connection elements.

SUMMARY OF THE INVENTION

It is an object of the invention is to provide an improved and more reliable power semiconductor device with a long service life.

This object is achieved by a power semiconductor device comprising a substrate and power semiconductor components disposed on, and connected to, the substrate. The inventive power semiconductor device further has a housing part, which includes a housing wall having a cutout. The power semiconductor device has a first load connection element, for making electrical contact with the power semiconductor device. The first load connection element passes through the cutout in the housing wall in an X direction, is electrically conductive, is formed in one piece and has a first outer connection section disposed outside the housing part and a first inner connection section disposed within the housing part. A first bush which is provided with an internal thread and runs in the X direction, is rotationally fixed and is movable in the X direction in the housing wall. The first outer connection section has a cutout, aligned with the first bush. The first load connection element has a first holding element disposed in the vicinity of the cutout in the housing wall, the holding element engaging a first groove in the housing wall, which groove runs perpendicular to the X direction.

It has proven advantageous if a second bush provided with an internal thread and running in the X direction is rotationally fixed and is immovable in the X direction in the housing wall. No outer connection section of a load connection element of the power semiconductor device is positioned outside the housing part in front of the second bush. The second bush is electrically insulated from the power semiconductor components. As a result, decoupling of the electrical connection between the power semiconductor device and the first busbar from the mechanical connection between the power semiconductor device and the first busbar is achieved.

Furthermore, it has proven to be advantageous if the power semiconductor device has, for making electrical contact with the power semiconductor device, a unitary second load connection element, which second load connection element runs through the cutout in the housing wall in the X direction, is electrically conductive and is electrically insulated from the first load connection element, and has a second outer connection section disposed outside the housing part and a second inner connection section disposed within the housing part. A second bush provided with an internal thread and running in the X direction is rotationally fixed and is substantially immovable in the X direction in the housing wall. The second outer connection section has a cutout aligned with the second bush. As a result, the occurrence of forces between the first and second outer connection sections which originate from tolerances of the thickness of the DC busbar and/or the spacing between the first and second outer connection sections in the X direction and/or the spacing between the DC busbar and the first and second outer connection sections is reliably avoided.

In addition, it has proven to be advantageous if the first load connection element has a third holding element, which is in the form of a section of the first load connection element disposed at the end of the first load connection element. The third holding element is disposed in a third groove in the housing wall, the third groove running generally perpendicular to the X direction, and has, on both sides in the X direction, a spacing from those walls of the housing wall which delimit the third groove. As a result, the possibility for movement of the first outer connection section of the first load connection element in the X direction is limited.

Furthermore, it has proven to be advantageous if the power semiconductor device has, for making electrical contact with the power semiconductor device, a second load connection element, which runs through the cutout in the housing wall in the X direction, is electrically conductive and is electrically insulated from the first load connection element, is formed in one piece and has a second outer connection section disposed outside the housing part and a second inner connection section disposed within the housing part. A second bush provided with an internal thread and running in the X direction is rotationally fixed and is movable in the X direction in the housing wall. The second outer connection section has a cutout aligned with the second bush. The second load connection element has a second holding element, which is disposed in the vicinity of the cutout in the housing wall and which engages in a second groove in the housing wall, the second groove running generally perpendicular to the X direction. As a result, the occurrence of forces between the first and second outer connection sections which originate from tolerances of the thickness of the DC busbar and/or the spacing between the first and second outer connection sections in the X direction and/or the spacing between the DC busbar and the first and second outer connection sections is reliably avoided.

In addition, it has proven to be advantageous if the first load connection element has a third holding element, which is in the form of a section of the first load connection element disposed at the end of the first load connection element. The third holding element is disposed in a third groove in the housing wall, the third groove runs generally perpendicular to the X direction, and has, on both sides in the X direction, a spacing from those walls of the housing wall which delimit the third groove, and/or if the second load connection element has a fourth holding element, which is in the form of a section of the second load connection element which is disposed at the end of the second load connection element. The fourth holding element is disposed in a fourth groove in the housing wall, the fourth groove running generally perpendicular to the X direction, and has, on both sides in the X direction, a spacing from those walls of the housing wall which delimit the fourth groove. As a result, the possibility for movement of the first or second outer connection section in the X direction is limited.

Furthermore, it has proven to be advantageous if the first bush is at least 10% further removed from a section of the first load connection element which runs in the X direction through the cutout in the housing wall than the second bush is removed from a section of the second load connection element which runs in the X direction through the cutout in the housing wall. As a result, the second outer connection section has more flexibility in the X direction.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1shows a perspective rear view of a power semiconductor device1according to the invention, andFIG. 2shows a detail view fromFIG. 1(the region bordered by dashed lines inFIG. 1).FIG. 3shows a perspective sectional illustration of power semiconductor device1according to the invention, wherein the front side of power semiconductor device1is illustrated on the left-hand side inFIG. 3.

Power semiconductor device1has a substrate20, on which power semiconductor components23are disposed and are connected to substrate20(seeFIG. 3). The respective power semiconductor component23is preferably in the form of a power semiconductor switch or a diode. The power semiconductor switches are in this case generally in the form of transistors, such as, for example, IGBTs (Insulated-Gate Bipolar Transistors) or MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors) or in the form of thyristors. Substrate20has an insulating body21(for example ceramic body) and an electrically conductive, structured first conduction layer, which is disposed on a first side of insulating body21and is connected to insulating body21and which forms, within the scope of the exemplary embodiment, conductor tracks22owing to its structure. Preferably, substrate20has an electrically conductive, preferably unstructured second conduction layer, wherein insulating body21is disposed between the structured first conduction layer and the second conduction layer. Substrate20, as in the exemplary embodiment, can be in the form of a direct copper bonded substrate (DCB substrate) or in the form of an insulated metal substrate (IMS), for example. The conductor tracks of the substrate can also be formed by electrically conductive leadframes, for example, which are disposed on an insulating body, such as an electrically nonconductive film, for example. The leadframes and the electrically nonconductive film to such an extent form a substrate. Power semiconductor components23are preferably cohesively connected (for example by a soldered or sintered layer) to conductor tracks22. For reasons of clarity, the soldered layer which connects power semiconductor components23to conductor tracks22cohesively is not illustrated inFIG. 3. As an alternative or in addition, power semiconductor components23can be connected to conductor tracks22by a compressive connection by virtue of, for example, a pressure being exerted on power semiconductor components23in the direction of conductor tracks22.

It will be mentioned that power semiconductor components23are electrically conductively connected to one another on their side remote from substrate20, by bonding wires and/or a film composite, for example, to one another and to conductor tracks22of substrate20, corresponding to the desired electrical circuit which is intended to be realized by power semiconductor device1. For reasons of clarity, these electrical connections are not illustrated inFIG. 3.

Substrate20is connected directly or indirectly to a metallic basic body14. Within the scope of the exemplary embodiment, metallic basic body14has a frame element14a,which passes around power semiconductor components23, and a base element14b,which is cohesively connected (for example by a welded joint) to frame element14a.Metallic basic body14within the scope of the exemplary embodiment is in the form of a liquid heat sink. Metallic basic body14could also be in the form of an air heat sink, for example, which preferably has cooling fins and/or cooling pins or in the form of a base plate which is intended for connection to an air or liquid heat sink. Metallic basic body14within the scope of the exemplary embodiment forms a channel27, through which a cooling liquid (for example water) flows. The cooling liquid enters or leaves channel27via openings30(seeFIG. 1). Substrate20within the scope of the exemplary embodiment is disposed on a cooling plate25which is provided with cooling pins26, which protrude into channel27, and which is connected to cooling plate25. Cooling plate25forms a cover for an opening of metallic basic body14and is connected to metallic basic body14. Substrate20is connected to metallic basic body14via cooling plate25.

Furthermore, power semiconductor device1has a housing part2, which is preferably unitary, i.e., formed in one piece, and which preferably runs laterally around power semiconductor components23. It will be mentioned here that housing part2does not necessarily run laterally around power semiconductor components23on the same plane on which power semiconductor components23are disposed, but can also run laterally around power semiconductor components23slightly above power semiconductor components23. Housing part2preferably consists of plastic.

The basic body14has a main outer surface which runs laterally around power semiconductor components23and which is at least partially covered areally by an elastic, electrically nonconductive, structured sealing element13which is formed in one piece and which runs laterally around power semiconductor components23.

Furthermore, power semiconductor device1preferably has driver circuits which are disposed on a printed circuit board24for actuating the power semiconductor switches.

It will be mentioned that, within the scope of the exemplary embodiment, a DC voltage is inverted into a three-phase AC voltage or a three-phase AC voltage is rectified into a DC voltage by power semiconductor device1. The following description in this case describes by way of example the design of power semiconductor device1as regards substrate20and the elements assigned to substrate20, with respect to the generation of a single-phase AC voltage. Substrate20within the scope of the exemplary embodiment is provided three times with an identical embodiment in such a way that, as already described above, a three-phase AC voltage is generated from a DC voltage or a three-phase AC voltage is rectified into a DC voltage by power semiconductor device1in the exemplary embodiment.

Housing part2has a housing wall10, which has a cutout40(seeFIGS. 1 and 2). Power semiconductor device1has a first load connection element3for making electrical contact with power semiconductor device1. First load connection element3runs through cutout40in housing wall10in a first, X, direction, is electrically conductive, is formed in one piece and has a first outer connection section3adisposed outside housing part2and a first inner connection section3bdisposed within housing part2. In order to make electrical contact with power semiconductor device1, the first outer connection section3ais connected to an electrically conductive first busbar31(see,FIG. 10). Load connection elements3are used for conducting load currents. The load currents which flow through load connection elements3in this case generally have a high current intensity in comparison with control currents which are used, for example, for actuating power semiconductor components when the power semiconductor components are in the form of power semiconductor switches. Furthermore, power semiconductor device1has electrically conductive connecting elements18, which connect substrate20, more precisely the first conduction layer of substrate20, to the electrically conductive load connection elements3. Load connection elements3can also be formed in one piece with the respectively assigned connecting elements18.

A first bush6which is provided with an internal thread and runs in the X direction is rotationally fixed and is movable in the X direction in housing wall10. For this purpose, housing wall10has an opening assigned to first bush6, wherein the geometric form of the inner wall of the opening corresponds to the geometric form of the circumference of first bush6, and the circumference of first bush6has edges. First bush6is connected in a form-fitting manner to housing wall10. First bush6is plugged into the opening assigned thereto.

The first outer connection section3aof first load connection element3has, aligned with first bush6, a cutout11. First outer connection section3ais preferably flexible in the X direction so that first outer connection section3ais movable slightly in the X direction with respect to a section3cof first load connection element3, section3crunning through cutout40in the X direction. Within the scope of the exemplary embodiment, the flexibility in the X direction of first outer connection section3ais achieved by virtue of the fact that first outer connection section3ahas a flat geometric form and is bent back, in particular bent back perpendicularly, with respect to section3cof first load connection element3. First outer connection section3apreferably forms, together with an intermediate section3dof first load connection element3, intermediate section3dis disposed between section3cof first load connection element3and first outer connection section3a,a u-shaped geometric form, which increases the flexibility in the X direction of first outer connection section3a.

First load connection element3has a first holding element8, which is disposed in the vicinity of cutout40in housing wall10and engages in a first groove9in housing wall10, groove9running generally perpendicular to the X direction. First load connection element3preferably has a further first holding element8′, which is disposed in the vicinity of cutout40in housing wall10and engages in a further first groove9′ in housing wall10, further first groove9′ running generally perpendicular to the X direction. The first or further first holding element8or8′ absorbs forces acting on first outer connection section3aof first load connection element3in the X direction and thereby prevents a movement of the first inner connection section3bin the X direction. In order to make electrical contact with power semiconductor device1, first outer connection section3ais connected to an electrically conductive first busbar31(seeFIG. 10), wherein the connection is preferably realized by a screw connection. For this purpose, first busbar31preferably has a cutout32. In order to realize the screw connection, the shaft of a screw is passed through cutout32in first busbar31and through cutout11in first outer connection section3aand the screw is screwed into first bush6. Forces acting on outer connection section3ain the X direction in the process are not transferred to first inner connection section3b,and also no forces acting in the X direction are transferred to housing part2since first bush6is movable in the X direction. Since first bush6is movable in the X direction, also no forces acting additionally in the X direction arise during tightening of the screw through first bush6, which forces would need to be absorbed by the first or further first holding element8or8′.

Existing tolerances of the elements involved and of the spacing between first outer connection section3aand first busbar31can thus be compensated for, wherein no movement of first inner connection section3boccurs or no forces act on first inner connection section3bin the X direction from the outside.

Preferably, a second bush7which is provided with an internal thread and runs in the X direction is rotationally fixed and is immovable in the X direction in housing wall10, wherein no outer connection section of a load connection element of power semiconductor device1is disposed outside housing part2in front of second bush7. Within the scope of the exemplary embodiment, second bush7is rotationally fixed and is immovable in the X direction by virtue of second bush7being cohesively connected to housing wall10(for example by virtue of it being injection-molded into the housing wall as well). Second bush7is electrically insulated from power semiconductor components23. First busbar31can be mechanically connected to power semiconductor device1, more precisely to housing part2of power semiconductor device1, by second bush7, while the electrically conductive connection between power semiconductor device1and first busbar31is realized by first bush6. As a result, decoupling of the electrical connection between power semiconductor device1and first busbar31from the mechanical connection between power semiconductor device1and first busbar31is achieved. For this purpose, first busbar31preferably has a further cutout32′. The shaft of a screw is passed through the further cutout32′ in first busbar31in order to realize the screw connection and the screw is screwed into second bush7.

FIG. 3shows, on the left-hand side, the front side of power semiconductor device1.FIG. 4shows a sectional view of a front-side detail of power semiconductor device1.FIG. 5shows a perspective illustration of a first and second load connection element3and4, wherein first load connection element3, in terms of its basic structure, is substantially designed as load connection element3shown inFIG. 2, and first bush6is designed and disposed as first bush6shown inFIG. 2.

Within the scope of the exemplary embodiment, power semiconductor device1has, for making electrical contact with power semiconductor device1, in addition, a second load connection element4, which runs through cutout40in housing wall10in the X direction, is electrically conductive and is electrically insulated from first load connection element3, is formed in one piece and has a second outer connection section4adisposed outside housing part2and a second inner connection section4bdisposed within housing part2. While first load connection element3shown inFIGS. 1 and 2is preferably used for connecting a busbar31having an AC voltage potential during operation, first load connection element3shown inFIG. 3andFIG. 4and second load connection element4shown inFIG. 3andFIG. 4are preferably used for connecting a DC busbar33(see,FIG. 11), which has a first busbar33having a first DC voltage potential (for example positive electrical potential) during operation and a second busbar35having a second DC voltage potential (for example negative electrical potential) during operation. An electrically nonconductive insulation layer37is disposed between first and second busbars33and35. DC busbar33has a cutout34running through first and second busbars33and35and through insulation layer37. Second busbar35has a cutout36.

A first bush6provided with an internal thread and running in the X direction is rotationally fixed and is movable in the X direction in housing wall10. For this purpose, housing wall10has an opening assigned to first bush6, wherein the geometric form of the inner wall of the opening corresponds to the geometric form of the circumference of first bush6, and the circumference of first bush6has edges. First bush6is connected in a form-fitting manner to housing wall10. First bush6is plugged into the opening assigned thereto.

Furthermore, a second bush7provided with an internal thread and running in the X direction is rotationally fixed and is immovable in the X direction in housing wall10, wherein second outer connection section4aof second load connection element4has, aligned with second bush7, a cutout15. Within the scope of the exemplary embodiment, second bush7is rotationally fixed and is immovable in the X direction by virtue of second bush7being cohesively connected to housing wall10(for example by virtue of it being injection-molded into the housing wall as well).

First outer connection section3ais preferably flexible in the X direction so that first outer connection section3ais slightly movable in the X direction with respect to a section3cof first load connection element3, section3crunning through cutout40in the X direction. Within the scope of the exemplary embodiment, the flexibility in the X direction of first outer connection section3ais achieved by virtue of the fact that first outer connection section3ahas a flat geometric form and is bent back, in particular bent back generally perpendicularly, with respect to section3cof first load connection element3.

Furthermore, second outer connection section4ais preferably flexible in the X direction so that second outer connection section4ais slightly movable in the X direction with respect to a section4cof second load connection element4, section4crunning through cutout40in the X direction. Within the scope of the exemplary embodiment, the flexibility in the X direction of second outer connection section4ais achieved by virtue of the fact that second outer connection section4ahas a flat geometric form and is bent back, in particular bent back generally perpendicularly, with respect to section4cof second load connection element4. Within the scope of the exemplary embodiment, the flexibility of second outer connection section4ain the X direction is increased by virtue of first bush6being at least 10%, in particular at least 20%, further removed from a section3cof first load connection element3, section3crunning through cutout40in housing wall10in the X direction, than second bush7is removed from a section4cof second load connection element4, section4crunning through cutout40in housing wall10in the X direction. First load connection element3therefore preferably has a larger outwardly leading lever arm than second load connection element4.

In order to make electrical contact with power semiconductor device1, first outer connection section3ais connected to electrically conductive first busbar33(seeFIG. 11), wherein the connection is preferably realized by a screw connection. In order to realize the screw connection, the shaft of a screw is passed through cutout34in DC busbar33and through cutout11in first outer connection section3a,and the screw is screwed into first bush6.

In order to make electrical contact with power semiconductor device1, furthermore, second outer connection section4ais connected to electrically conductive second busbar35(see,FIG. 11), wherein the connection is preferably realized by a screw connection. In order to realize the screw connection, the shaft of a screw is passed through cutout36in second busbar35and through cutout15in second outer connection section4a,and the screw is screwed into second bush7.

Forces acting on outer connection section3ain the X direction in the process are not transferred to the first inner connection section3b,and also no forces acting in the X direction are transferred to housing part2since first bush6is movable in the X direction. Since first bush6is movable in the X direction, no forces acting additionally in the X direction are produced during tightening of the screw through first bush6which would need to be absorbed by first or further first holding element8or8′ of first load connection element3.

Existing tolerances of the elements involved and the spacing between the first and second outer connection sections3aand4aand DC busbar33can be compensated for hereby, wherein no movement of first and second inner connection sections3band4barises or no forces act on the first and second inner connection sections3aand3bin the X direction from the outside. In particular, as a result the occurrence of forces between the first and second outer connection sections3aand4awhich originate from tolerances of the thickness of DC busbar33and/or the spacing between the first and second outer connection sections3aand4ain the X direction and/or the spacing between DC busbar33and first and second outer connection sections3aand4ais reliably avoided.

Preferably, as illustrated by way of example inFIG. 6, the sections3cand4cof first and second load connection elements3and4, said sections running in the X direction through cutout40, are surrounded by an electrically nonconductive elastomer16so that a load connection apparatus50having first and second load connection elements3and4and elastomer16is in the form of a structural unit. Elastomer16fills the gap17provided between first and second load connection elements3and4. Elastomer16is preferably in the form of silicone. The silicone is preferably in the form of a crosslinked liquid silicone rubber or in the form of a crosslinked solid silicone rubber. Load connection apparatuses50are introduced into the cutouts40during fitting of power semiconductor device1.

FIG. 7shows a sectional view of a front-side detail of a further power semiconductor device1according to the invention.FIG. 8shows a perspective illustration of a first and second load connection element3and4of the further power semiconductor device1according to the invention, andFIG. 9shows a perspective illustration of the first and second load connection elements3and4of the further power semiconductor device1according to the invention which are laterally surrounded by an electrically nonconductive elastomer. The further power semiconductor device1according to the invention shown inFIG. 7corresponds to the power semiconductor devices1described in connection withFIGS. 3 to 6(including described possible advantageous embodiments) apart from the feature that first load connection element3has a third holding element19, which is in the form of a section of first load connection element3which is disposed at the end of first load connection element3, wherein third holding element19is disposed in a third groove53in housing wall10, third groove53running generally perpendicular to the X direction, and has, on both sides in the X direction, a spacing from those walls51and52of housing wall10which delimit third groove53. Third holding element19limits, in the X direction, the possible movement of first outer connection section3aof first load connection element3.

FIG. 12shows a sectional view of a front-side detail of a further power semiconductor device1according to the invention. The further power semiconductor device1according to the invention shown inFIG. 12corresponds to the power semiconductor devices1described in connection withFIGS. 3 to 7(including described possible advantageous embodiments) apart from the features that second bush7is movable in the X direction and second load connection element4has a second holding element61, which is disposed in the vicinity of cutout40in housing wall10and engages in a second groove62in housing wall10, second groove62running generally perpendicularly to the X direction.

Second load connection element4shown inFIG. 12preferably has, similarly to the embodiment illustrated by way of example inFIG. 8, a further second holding element (not shown inFIG. 12), which is disposed in the vicinity of cutout40in housing wall10and engages in second groove62in housing wall10. Second holding element61or the further second holding element absorbs forces acting on second outer connection section4aof second load connection element4in the X direction and thereby prevents a movement of second inner connection section4bin the X direction.

Furthermore, also in the case of power semiconductor device1shown inFIG. 12, first load connection element3can have a third holding element19, which is in the form of a section of the first load connection element2which is disposed at the end of first load connection element2, wherein third holding element19is disposed in a third groove53in housing wall10, third groove53running generally perpendicularly to the X direction, and has, on both sides in the X direction, a spacing from those walls of housing wall10which delimit third groove53. As an alternative or in addition, second load connection element4, analogously to first load connection element3, can have a fourth holding element (not illustrated inFIG. 12for reasons of clarity), which is in the form of a section of second load connection element4which is disposed at the end of second load connection element4, wherein the fourth holding element is disposed in a fourth groove (not illustrated inFIG. 12for reasons of clarity) in housing wall10, said fourth groove running generally perpendicularly to the X direction, and has, on both sides in the X direction, a spacing from those walls of the housing wall which delimit the fourth groove.

Preferably, the first, further first, second, third and fourth grooves in housing wall10run in the Z direction.

It will furthermore be mentioned that first and second load connection elements3and4, respectively, are preferably in the form of multiply bent-back sheet-metal elements.

Furthermore, it will be mentioned that the first and second busbars are preferably in the form of sheet-metal elements.

In addition, it will be mentioned that the housing of the power semiconductor device can consist only of the housing part or can have still further housing parts.

It will be mentioned at this juncture that features of various exemplary embodiments of the invention, insofar as the features are not mutually exclusive, can of course be combined with one another as desired.

In the preceding Detailed Description, reference was made to the accompanying drawings, which form a part of this disclosure, and in which are shown illustrative specific embodiments of the invention. In this regard, directional terminology, such as “top”, “bottom”, “left”, “right”, “front”, “back”, etc., is used with reference to the orientation of the Figure(s) with which such terms are used. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of ease of understanding and illustration only and is not to be considered limiting.