Printed circuit board arrangement

Abstract

A printed circuit board 1 having upper 11 and lower sides 12 preferably provides a solid state pawer controller SSPC (see schematics of figs 11, 12) that uses multiple semiconductor switches 21, prefe

Description

Field The present disclosure relates to a printed circuit board arrangement and to a method for manufacturing such printed circuit board arrangement. Background With increased penetration of electrical systems and the progression towards full electric and hybrid propulsion systems, the use of energy storage systems and DC power distribution has gained increased use. Multiple loads and sources may be connected to a DC distribution system such as a hybrid propulsion system. In such system, adequate DC protection devices are required. Due to the fact that SSPCs (Solid State Power Controllers) show a fast response time, eliminate arcing during turn-off, and have a high reliability, SSPCs are preferred over electro-mechanical switches. To improve power density in a DC distribution system there is a trend to move away from traditional power module-based power converter designs to power converter designs in which of the semiconductor switches are mounted on a printed circuit board (PCB), wherein a plurality of semiconductor switches may be arranged in parallel to achieve a high power level and current carrying capability. Sufficient cooling of the semiconductor switch is a key element of the design and required in order to keep the junction temperature of the semiconductor switches well below a maximum allowable limit. SiC MOSFETs TO-247 packages are popular semiconductor switches and there is a desire to use such semiconductor switches in SSPCs or other power systems that require semiconductor switches. TO-247 packages (Transistor Outline 247, defined by JEDEC (Joint Electron Device Engineering Council) is a family of through-hole 3-leaded component packages commonly used for devices that dissipate significant thermal power. However, TO-247 packages are facing challenges in terms of thermal management, and most failure modes mechanism are related to overheating and thermal cycling effects which cause mechanical stress due to thermal expansion of bonded material. The same is true for other TO packaged semiconductor switches. There is thus a desire to build printed circuit board based power devices with TO packaged semiconductor switches which receive effective cooling. There is a need to provide a printed circuit board arrangement that comprises semiconductor switches formed as TO-packages that receive effective cooling and can be manufactured in an effective manner. Summary In a first aspect a printed circuit board arrangement is provided. The printed circuit board arrangement comprises a printed circuit board that has an upper (top) side and a lower (bottom) side. The printed circuit board arrangement further comprises a plurality of semiconductor switches formed as TO packages that are arranged at the lower side of the printed circuit board. The TO packages each have a body and connecting legs. The connecting legs are connected to the printed circuit board and extend perpendicular to the lower side of the printed circuit board. The bodies of the TO packages are bent 90 degrees with respect to their connecting legs (such that they side faces run parallel to the lower side of the printed circuit board). There is further provided at least one holding down clamp that extends between the lower side of the printed circuit board and the 90 degrees bent TO package bodies, and a heat sink arranged below the bent TO package bodies, wherein the heat sink has an upper side. The holding down clamp is configured to press the TO package bodies against the upper side of the heat sink. Aspects of the disclosure are thus based on the idea to improve the cooling of TO packaged semiconductor switches in that the TO package bodies are pressed against a heat sink by means of one or several holding down clamps. To allow that the TO package bodies can be pressed against the heat sink, they are bent 90 degrees with respect to their connecting legs. Thereby, they are brought in a position that allows that one of the side faces of the TO package bodies can be pressed by means of the holding down clamp against the heat sink, thereby improving heat transfer from the TO package body into the heat sink. An improved thermal stability across the discrete devices is provided for that leads to longer reliability and lifetime. Besides improving heat transfer into a heat sink, the present disclosure is also associated with the advantage that the inventive concept may be implemented in practical serial manufacturing, with the ability to automate the manufacturing with good repeatability. The present disclosure is applicable for all kind of TO packaged semiconductor switches. Examples include MOSFET, IGBT, SiC FETs, and GaN FETs. It is pointed out that, within the meaning of the present disclosure, that side of the printed circuit board at which the semiconductor switches are arranged is defined to be the lower side of the printed circuit board, irrespective of the actual orientation of the circuit board in space. In some embodiments, the holding down clamp is connected directly or indirectly to the heat sink. This allows the holding down clamp to exert a pressure on the TO package bodies. In some embodiments, the holding down clamp is connected indirectly to the heat sink, wherein a clamp counterstructure is arranged at the bottom side of the heat sink and comprises protruding areas which extend beyond the lateral edges of the heat sink, wherein the protruding areas are configured to be connected to the holding down clamp. By connecting to a clamp counterstructure instead of the heat sink itself, the provision of holes or the like in the heat sink that potentially reduce the effectiveness of cooling and may violate creepage and clearance requirements can be avoided. In some embodiments, the holding down clamp comprises a flat main part which extends at a distance from the upper side of the heat sink (such that the TO package bodies can be arranged between the flat main part and the heat sink) and further comprises angled end parts which comprise support points to connect the holding down clamp directly or indirectly to the heat sink. For example, the flat main part is rectangular, wherein two angled end parts with support points are formed at the two ends of the rectangular main part. The rectangular main part may be formed similar as a bar or beam, wherein it has a flat side at least towards the TO package bodies. In some embodiments, the angled end parts are screwed to protruding areas of the mentioned clamp counterstructure. The holding down clamp may be made of any sufficiently stiff material that allows to exert a pressure onto the bodies of the TO packages. Example materials are polyamides, polyimides or aluminum. In case of aluminum or another metal, the holding down clamp may be a sheet metal part. A conformal coating may be provided with the clamp. The plurality of semiconductor switches may be arranged in one row or several parallel rows at the lower side of the printed circuit board. Holding down clamps may be provided in accordance with the number of rows of semiconductor switches, wherein each holding down clamp is configured to press the semiconductor switches of one row against the upper side of the heat sink. In some embodiments, the connecting legs of the TO package are soldered both to the lower side and to the upper side of the printed circuit board. By soldering the connecting legs at both sides and thus providing solder joints at both sides, the quality of the soldering with the printed circuit board is improved. The printed circuit board may be a thick copper printed circuit board, wherein the thickness of the copper layers may be in the range between 3oz and 6oz. The use of a thick copper printed circuit board allows to implement higher currents. In some embodiments, a thermal interface material is arranged between the TO package bodies and the upper side of the heat sink. Such thermal interface material may be a thermal pad, a thermal paste, or the like. When used in combination with a clamp counterstructure for attaching the holding down clamp, the advantage exists that the thermal interface material does not need to be punched, thereby reducing the risk of insulation failure, and the risk of compromise creepage and clearance. The TO packages may be TO-247 packages, e.g., SiC MOSFETs TO-247 packages. However, the present disclosure is suitable for any TO package in which the package body has side faces which may be pressed against the heat sink by means of a holding down clamp. The semiconductor switches of the printed circuit board arrangement may be arranged and contacted in a manner such that the semiconductor switches form part of a solid state power controller. For example, the semiconductor switches may form at least one switching unit of the solid state power controller, wherein each of the at least one switching units comprises a plurality of semiconductor switches arranged in parallel. However, the printed circuit board arrangement of the present disclosure is not limited to any specific implementation of the semiconductor switches and may be provided to implement other circuits with semiconductor switches as well. In a second aspect a solid state power controller for a DC power distribution and protection system is provided. The solid state power controller comprises at least one first switching unit arranged in a positive voltage rail of the DC power distribution and protection system, wherein the at least one switching unit comprises a plurality of semiconductor switches arranged in parallel, and / or the solid state power controller comprises at least one second switching unit arranged in a negative voltage rail of the DC power distribution and protection system, wherein the at least one switching unit comprises a plurality of semiconductor switches arranged in parallel. Further, a printed circuit board is provided, wherein the semiconductor switches are formed as TO packages and connected to the printed circuit board to form a printed circuit board assembly in accordance with the present disclosure. This aspect of the disclosure implements a solid state power controller by means of a printed circuit board arrangement that is in accordance with the present disclosure. In a third aspect a method of manufacturing a printed circuit board arrangement is provided. The method comprises the steps of: providing a printed circuit board having an upper side and a lower side; providing a plurality of semiconductor switches formed as a TO packages, the TO packages having a body and connecting legs; bending the TO package bodies 90 degrees with respect to the connecting legs; fixing the TO package bodies at at least one holding down clamp; arranging the holding down clamp and the TO package bodies at the lower side of the printed circuit board, wherein the holding down clamp is arranged between the lower side of the printed circuit board and the TO package bodies; electrically connecting the connecting legs of the TO packages to the printed circuit board; connecting the holding down clamp to a heat sink or a structure connected to the heat sink; and pressing the TO package bodies against an upper side of the heat sink through the holding down clamp. The method is based on the idea to bend the bodies of the TO packages 90 degrees with respect to the connecting legs, such that the opportunity is provided to press the TO package bodies against a heat sink by means of a holding down clamp. In some embodiments, the holding down clamp is connected to a clamp counterstructure arranged at the bottom side of the heat sink, thereby avoiding manipulation of the heat sink or of a thermal interface material attached to the heat sink. In some embodiments, the connecting legs of the TO packages are soldered both to the lower side and to the upper side of the printed circuit board to provide for an improved electrical connection. In some embodiments, the semiconductor switches are arranged in one row or several parallel rows, wherein holding down clamps are provided in accordance with the number of rows of semiconductor switches, and wherein each holding down clamp presses the semiconductor switches of one row against the upper side of the heat sink. The skilled person will appreciate that except where mutually exclusive, a feature or parameter described in relation to any one of the above aspects may be applied to any other aspect. Furthermore, except where mutually exclusive, any feature or parameter described herein may be applied to any aspect and / or combined with any other feature or parameter described herein. Brief description of the drawings The invention will be explained in more detail on the basis of exemplary embodiments with reference to the accompanying drawings in which: FIG. 1 is a schematic side view of a printed circuit board arrangement which comprises semiconductor switches formed as a TO packages, wherein a body of the TO packages is bent 90 degrees with respect to connecting legs of the TO package, and wherein the TO package bodies are pressed by means of a holding clamp against a heat sink; FIG. 2 depicts in a front view, a rear view and a side view a TO package; FIG. 3 is a view on the inner side of a holding down clamp; FIG. 4 is a view on the inner side of a holding down clamp, wherein a plurality of TO package bodies are attached to the inner side; FIG. 5 is a bottom view on the lower side of a printed circuit board, wherein a plurality of semiconductor switches formed as TO packages are attached with their connecting legs to the lower side of the printed circuit board, and wherein holding down clamps are arranged between the lower side of the printed circuit board and rows of TO package bodies; FIG. 6 shows a section of the printed circuit board assembly of FIG. 5 with six semiconductor switches forming one switching unit: FIG. 7 is a top view on a heat sink, wherein a thermal interface material is arranged on the upper side of the heat sink; FIG. 8 is a top view on a printed circuit board arrangement, wherein a printed circuit board is arranged with this lower side on the heat sink and thermal interface material of FIG. 7; FIG. 9 is a bottom view of the heat sink of FIGS. 7 and 8, wherein clamp counterstructures are arranged on the bottom side of the heat sink; FIG. 10 is a flowchart of a method for manufacturing a printed circuit board arrangement; FIG. 11 is a schematic depiction of a solid state power controller; FIG. 12 is an embodiment of a solid state power controller which comprises switching units both in a positive voltage rail and a negative voltage rail; FIG. 13 shows a TO-247 semiconductor package; and FIG. 14 illustrates a prior art connection of a TO-247 semiconductor package to a heat sink. Detailed description Before discussing embodiments of the present disclosure with respect to FIGS. 1 to 10, the background of the disclosure is discussed with respect to FIGS. 11 to 14 to provide for a better understanding of the present disclosure. FIG. 11 shows a DC power distribution and protection system that comprises a unidirectional solid state power controller 100, in the following referred to as SSPC. The system comprises a DC power source 5 (such as a DC battery) that has a positive terminal 51 and a negative terminal 52. Between the positive terminal 51 and the negative terminal 52 a battery voltage Vdc is present (which, in embodiments, may be in the range between 450 and 850 V). A positive voltage rail 6 is connected to the positive terminal 51 and a negative voltage rail 7 is connected to the negative terminal 52. The positive voltage rail 6 and the negative voltage rail 7 form a high-voltage bus. The system further comprises a load R, wherein the load R may be formed in a plurality of manners. In examples, the load may be a power converter such as an inverter and / or an electric motor. A capacitive load generally depicted as Co is arranged in parallel to the load R and extends between the positive voltage rail 6 and the negative voltage rail 7. For example, the capacitive load may be formed by DC link capacitors or include such capacitors. The SSPC 100 comprises a semiconductor switch S1 with an antiparallel bypass diode D1 arranged in the positive voltage rail 3. The switch S1 may be a MOSFET (metal-oxide-semiconductor field-effect transistor), GaN (Gallium Nitride), SiC (Silicon Carbide) or IGBT (Insulated Gate Bipolar Transistor) switch. A further diode D may extend between the positive voltage rail 5 and the negative voltage rail 6. Further, optionally, a transient voltage suppressor diode TVS may extend in parallel to the semiconductor switch S1. The SSPC 100 further comprises a gate driver 110 that is responsible for controlling the switching of the semiconductor switch S1 and provides the necessary gate signal to the gate of semiconductor switch S1. The SSPC 100 may also comprise a microcontroller (not shown) for control of the logic. FIG. 12 depicts DC power distribution and protection system with the same basic arrangement as the system of FIG. 11. Accordingly, the DC power distribution and protection system comprises a DC power source 5 having a positive terminal 51 and a negative terminal 52, a power bus having a positive voltage rail 6 and a negative voltage rail 7, an SSPC 100, a load R, a capacitive load Co, and several inductances L1-L4, wherein inductances L1, L2 are arranged in the positive voltage rail 3 and inductances L3, L4 are arranged in the negative voltage rail 4. In FIG. 12, the SSPC 100 comprises two switching units S1, S2 in the positive voltage rail and two switching units S3, S4 in the negative voltage rail 7, wherein each of the switching units comprises a plurality of semiconductor switches S11-S16, S21-S26, S31-S36, S41-S46 which are arranged in parallel. Accordingly, a bidirectional SSPC is implemented both in the positive voltage rail 6 and the negative voltage rail 7. Each of the semiconductor switches S11-S16, S21-S26, S31-S36, S41-S46 comprises a transistor and a bypass diode as discussed with respect to FIG. 11. The SSPC 100 further comprises gate drivers for the different switching units S1 to S4 (not shown). The gate drivers may be commercially available off-the-shelf gate drivers in embodiments. In other embodiments, the SSPC comprises one or two switching units only in the positive voltage rail or only in the negative voltage rail, wherein the switching unit or switching units comprise a plurality of semiconductor switches arranged in parallel. By paralleling a plurality of semiconductor switches S11-S16, S21-S26, S31-S36, S41-S46 in the switching instances S1-S4, the current capacity can be increased and / or voltage drop and power loss can be reduced. There is a desire to implement an SSPC of the kind shown in FIGS. 11 and 12 by means of semiconductor switches which are implemented as TO packages, such as TO-247 packages. FIG. 13 shows a semiconductor switch 2 formed by a TO-247 package. The TO package 2 comprises a body 21 and connecting legs 22. In the depicted example, the TO package 2 comprises three connecting legs 22, wherein there may be provided four connecting legs in other examples. The connecting legs are soldered with a solder joint 220 to a printed circuit board 1. The body 21 has an approximately cuboid shape and comprises flat side faces 23, 24 arranged in parallel to each other. When used in a power device such as an SSPC, the TO packages 2 need to be cooled. FIG. 14 depicts a prior art configuration for cooling the TO packages. A heat sink 4’ is arranged perpendicularly to a printed circuit board 1. The TO package 2 is connected by means of solder joints 220 with the connecting legs 22 to the printed circuit board 1. One of the side faces 24 of the TO package body 21 rests against the heat sink 4’. However, to connect the body 21 to the heat sink 4’, a rigid extension 27 of the TO package 2 is required that can be screwed against the heat sink 4’. This, however, is compromising insulation coordination and makes it difficult to meet creepage and clearance requirements. Also, a perpendicular arrangement of the heat sink with respect to the printed circuit board 1 is required which may not be convenient. FIG. 1 is a slightly perspective side view of an embodiment of a printed circuit board arrangement in accordance with the present disclosure. The printed circuit board arrangement comprises a printed circuit board 1 that has an upper side 11 and a lower side to 12. The printed circuit board 1 may be a thick copper printed circuit board. A plurality of semiconductor switches 2 are arranged on the lower side 12 of the printed circuit board 1. The semiconductor switches 2 are of the TO package type. Accordingly, they comprise a body 21 and connecting legs 22. It is provided that the bodies 21 of the TO packages 2 are bent 90 degrees with respect to their connecting legs 22. The connecting legs 22 are electrically connected to the printed circuit board 1, wherein they are soldered both to the lower side 12 and the upper side 12 of the printed circuit board 1 for optimal electrical connection. The bodies 21 of the TO packages 2, due to their bending by 90 degrees, have a side face 23 which runs parallel both to the lower side 12 of the printed circuit board 1 and a flat upper side 41 of a heat sink 4. The heat sink 4 is generally located below the TO package bodies 21 and comprises the flat upper side 41 and a lower side 42, which is also flat in the depicted embodiment but may have other shapes as well. The arrangement further comprises several holding down clamps 3, which in FIG. 1 are depicted essentially from their sides. The construction of the holding down clamps 3 will discussed in detail with respect to FIGS. 3 and 4. The holding down clamps 3 each comprise a flat main part 30 which extends at a distance from the upper side 41 of the heat sink 4 and is located between the lower side 12 of the printed circuit board 1 and the TO package bodies 21. The holding down clamps 3 further each comprises end parts 31 which are connected by a screw 36 to a clamp counterstructure 35 which will be explained in more detail with respect to FIG. 9. There is further provided a thermal interface material 8 which extends on the upper side 41 of the printed circuit board. By connecting to the clamp counterstructure 350, the holding down clamp 3 exerts a force on the top side face of the TO package bodies 21 and presses the TO package bodies 21 with their bottom side face (through the thermal interface material 8) against the upper side 41 of the heat sink 4. This way, the TO package bodies 21 are efficiently thermally coupled to the heat sink 4, with the heat of the TO package bodies 21 dissipating into the heat sink 4. It is pointed out that the heat sink 4 is depicted schematically only. For example, the heat sink 4 may be actively or passively cooled. Also, there may be cooling fins of the heat sink. The heat sink 4 may be made of aluminum or another metal or metal alloy. The printed circuit board arrangement of FIG. 1 is further explained by discussing some of its elements with respect to FIGS. 2 to 9. FIG. 2 shows a TO package 2 similar to the TO package of FIG. 13 in a front view, a rear view and a side view, wherein the legs 22 are bent by 90 degrees with respect to the body 21. More particularly, the legs 22 each comprise a portion 221 in line with the body 21 and a portion 222 bent by 90 degrees. FIG. 3 depicts the clamp 3 of the arrangement of FIG. 1. The clamp 3 comprises a flat main part 30 which, in the assembled configuration, extends at a distance from the upper side 41 of the heat sink 4 (see FIG. 1). The flat main part 30 is rectangular. Further, there are provided two end parts 31, 32, each one at one of the ends of the rectangular main part 30. The end parts 31, 32 are angled. They comprise a vertical section 311, 321 and a flat section 312, 322, wherein support points 33 in the form of holes are provided in the flat sections 312, 322. In these holes the screws 36 of FIG. 1 are arranged. In other embodiments, the end parts 31, 32 may be formed differently such as by curved sections. In each case, the support points 33 may be arranged in a plane which is at a distance from the plane in which the main part 30 extends, such that a pressure on the semiconductor switches can be easily produced. FIG. 3 also depicts small structures 38 in the main part 30 which allow to adjust TO packages. In FIG. 4, TO packages 2 are fixed to the inner side of the main rectangular part 30 of the clamp 3, wherein such fixing may be through the structures 38. The connection between the TO packages 2 and the inner side of the clamp 30 does not need to be very firm, as the TO packages 2 are pressed against the heat sink 4 by means of the clamp 3 anyway, see FIG. 1. It is pointed out that, in FIG. 4, the connecting legs 22 of the TO packages 2 have already been bent by 90 degrees. FIG. 5 is a top perspective view on the lower side 12 of the printed circuit board 1, wherein a plurality of semiconductor switches 2 are arranged at the lower side 12 in four parallel rows A-D. The semiconductor switches are formed as TO packages 2 with bent connecting legs 22 as discussed. Holding down clamps 3 as shown in FIG. 4 have been placed above the lower side 12 of the printed circuit board 1, wherein the TO package bodies 21 rest flat with their upper face (side face 24 in FIG. 2) against the holding down clamps 3. Each holding down clamp 3, accordingly, is arranged between the lower side 12 of the printed circuit board 1 and the TO package bodies 21. In such a configuration, the printed circuit board 1 with the TO packages 2 and the holding down clamp 3 can be attached to a heat sink, as will be discussed with respect to FIGS. 7 to 9. Holding down clamps 3 are provided in accordance with the number of rows A-D of the semiconductor switches 2, such that there are provided four holding down clamps 3 in the depicted embodiment, each holding down clamp pressing one row of semiconductor switches against the heat sink in the finally assembled state. FIG. 6 shows a section of the printed circuit board assembly of FIG. 5, wherein six semiconductor switches 2 are depicted which, together, are such connected through the printed circuit board that they form a switching unit such as switching unit S1 of the SSPC 100 of FIG. 12. The other semiconductor switches of FIG. 5 may form a second, third and fourth switching unit S2, S3, S4 such that the arrangement of FIG. 5 realizes the semiconductor switches of switching units S1, S2, S3, S4 of the SPC 100 of FIG. 12. FIG. 7 is a top view on an embodiment of a heat sink 4. A cooling coil 9 may extend through the heat sink 4. The heat sink 4 has a upper side 41. A thermal interface material 8 is located on the upper side 41 of the heat sink 4. FIG. 8 is a top view on a printed circuit board arrangement similar to the arrangement of FIG. 1, wherein the arrangement of FIG. 5 has been placed on the upper side 41 of heat sink 4 and the thermal interface material 8. As FIG. 8 is a top view on the upper side 11 of the printed circuit board 1, the semiconductor switches and the holding down clamps of FIG. 5 cannot be seen. FIG. 9 is a bottom view of the heat sink 4 and illustrates how the holding down clamps 3 may be indirectly attached to the heat sink 4, which is required for being able to press the TO package bodies 21 against the heat sink 4. According to FIG. 9, a clamp counterstructure 35 is arranged at the bottom side 42 of the heat sink 4. The clamp counterstructure 35 is formed by flat rectangular bars which each comprise a protruding area 350 which extends beyond the lateral edges 45 of the heat sink 4. In the protruding areas 350, a screwing hole 360 or the like is formed. Referring again to FIGS. 1, 3 and 4, the screws 36 are screwed through the openings 33 of the end parts 31, 32 of the holding down clamp 3 into the holes 360 of the clamp counterstructure 35, thereby providing for a firm connection between the holding down clamp 3 and the clamp counterstructure 35. At the same time, by such connection, the holding down clamp 3 is connected to the heat sink 4 in the sense that it is allowed to exert a pressure against the heat sink 4. In other embodiments, the holding down clamp 3 may be attached directly to side areas of the heat sink 4, wherein such side areas could be to the side of the thermal interface material 8. The printed circuit board arrangement allows to efficiently cool the TO package semiconductor switches in that a flat face of the TO package bodies is pressed against the heat sink, thereby increasing a heat conduction from the TO package bodies into the heat sink. FIG. 10 is a flowchart of the steps to manufacture a printed circuit board arrangement in accordance with FIG. 1. In step 101, a printed circuit board having an upper side and a lower side is provided. In step 102, a plurality of semiconductor switches formed as TO packages are provided. In step 103, the TO package bodies are bent 90 degrees with respect to the TO package connecting legs, as shown in FIG. 2. In step 104, the TO package bodies are fixed at one or several holding down clamps, as shown in FIG. 4. Subsequently, in step 105, the holding down clamp and the TO package bodies are arranged at the lower side of the printed circuit board, wherein the holding down clamp is arranged between the lower side of the printed circuit board and the TO package bodies, as shown in FIG. 5. The connecting legs of the TO packages are then electrically connected to the printed circuit board in step 106. To this end, the TO packages may be soldered both to the lower side and the upper side of the printed circuit board, as shown in FIG. 1. The holding down clamp (together with the printed circuit board) is then in step 107 connected to a heat sink or a structure connected to the heat sink, such as the clamp counterstructure of FIG. 9. In step 108, the TO package bodies are pressed against the upper side of the heatsink through the holding down clamp that has been connected to the clamp counterstructure. A plurality of semiconductor switches may be arranged in one or several rows as shown in FIG. 5, wherein holding down clamps are provided in accordance with the number of rows and wherein each holding down clamp presses the semiconductor switches of one row against the upper side of the heat sink. However, in other embodiment, a single, large area (such as square) holding down clamp may be provided that contacts all semiconductor switches. It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. 5 Also, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. Various features of the various embodiments disclosed herein can be combined in different combinations to create new embodiments 10 within the scope of the present disclosure. In particular, the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein. Any ranges given herein include any and all specific values within the range and any and all sub-ranges within the given range. 15

Claims

1. A printed circuit board arrangement comprising:a printed circuit board (1) having an upper side (11) and a lower side (12);a plurality of semiconductor switches (2) formed as TO packages that are arranged at the lower side (12) of the printed circuit board (1), the TO packages (2) having a body (21) and connecting legs (22), wherein the connecting legs (22) are connected to the printed circuit board (1) and extend perpendicular to the lower side (12) of the printed circuit board (1), and the bodies (21) of the TO packages are bent 90 degrees with respect to their connecting legs (22);at least one holding down clamp (3) extending between the lower side (12) of the printed circuit board (1) and the 90 degrees bent TO package bodies (21); anda heat sink (4) arranged below the TO package bodies (21), the heat sink (4) having an upper side (41);wherein the holding down clamp (3) is configured to press the bent TO package bodies (21) against the upper side (41) of the heat sink (4).

2. The printed circuit board arrangement of claim 1, wherein the holding down clamp (3) is connected directly or indirectly to the heat sink (4).

3. The printed circuit board arrangement of claim 2, wherein the holding down clamp (3) is connected indirectly to the heat sink (4), wherein a clamp (3) counterstructure (35) is arranged at a bottom side (42) of the heat sink (4) and comprises protruding areas (350) which extend beyond lateral edges (45) of the heat sink (4), wherein the protruding areas (350) are configured to be connected to the holding down clamp (3).

4. The printed circuit board arrangement of any preceding claim, wherein the holding down clamp (3) comprises a flat main part (30) which extends at a distance from the upper side (41) of the heat sink (4) and angled end parts (31, 32) which comprise support points (33) to connect the holding down clamp (3) directly or indirectly to the heat sink (4).

5. The printed circuit board arrangement of claim 4, wherein the flat main part (30) is rectangular, wherein two angled end parts (31, 32) with support points (33) are formed at the two ends of the rectangular main part (30).

6. The printed circuit board arrangement of claim 5, when dependant on claim 3, wherein the angled end parts (31, 32) are screwed to protruding areas (350) of the clamp counterstructure (35).

7. The printed circuit board arrangement of any preceding claim, wherein the holding down clamp (3) is made of polyamides, polyimides, or aluminum.

8. The printed circuit board arrangement of any preceding claim, wherein the plurality of semiconductor switches (2) is arranged in one row (A) or several parallel rows (A-D).

9. The printed circuit board arrangement of claim 8, wherein holding down clamps (3) are present in accordance with the number of rows (A-D) of semiconductor switches (2), wherein each holding down clamp (3) is configured to press the semiconductor switches of one row (A-D) against the upper side (41) of the heat sink (4).

10. The printed circuit board arrangement of any preceding claim, wherein the connecting legs (22) of the TO package (2) are soldered both to the lower side (12) and to the upper side (11) of the printed circuit board (1).

11. The printed circuit board arrangement of any preceding claim, wherein the printed circuit board (1) is thick copper printed circuit board.

12. The printed circuit board arrangement of any preceding claim, wherein a thermal interface material (379 ) is arranged between the TO package bodies (21) and the upper side (41) of the heat sink (4).

13. The printed circuit board arrangement of any preceding claim, wherein the TO packages are TO-247 packages.

14. The printed circuit board arrangement of any preceding claim, wherein the semiconductor switches (2) are configured to form part of a solid state power controller (100).

15. The printed circuit board arrangement of claim 14, wherein the semiconductor switches (2) form at least one switching unit (S1-S4) of the solid state power controller, wherein each of the at least one switching units (S1-S4) comprises a plurality of semiconductor switches (S11-S16, S21-S26, S31-S36, S41-S46) arranged in parallel.

16. A solid state power controller for a DC power distribution and protection system, the solid state power controller comprising:at least one first switching unit (S1, S2) arranged in a positive voltage rail (6) of the DC power distribution and protection system, wherein the at least one switching unit (S1, S2) comprises a plurality of semiconductor switches (S11-S16, S21-S26) arranged in parallel; and / orat least one second switching unit (S3, S4) arranged in a negative voltage rail (7) of the DC power distribution and protection system, wherein the at least one switching unit (S3, S4) comprises a plurality of semiconductor switches (S31-S36, S41-S46) arranged in parallel; anda printed circuit board (1);wherein the semiconductor switches (S11-S16, S21-S26, S31-S36, S41-S46) are formed as TO packages (2) and connected to the printed circuit board (1) to form a printed circuit board assembly of any preceding claim.

17. A method of manufacturing a printed circuit board arrangement, the method comprising the steps of:providing (101) a printed circuit board (1) having an upper side (11) and a lower side (12);providing (102) a plurality of semiconductor switches (2) formed as TO packages, the TO packages (2) having a body (21) and connecting legs (22);bending (103) the TO package bodies (21) 90 degrees with respect to the connecting legs (22);fixing (104) the TO package bodies (21) at at least one holding down clamp (3);arranging (105) the holding down clamp (3) and the TO package bodies (21) at the lower side of the printed circuit board (1), wherein the holding down clamp (3) is arranged between the lower side (12) of the printed circuit board (1) and the TO package bodies (21);electrically connecting (106) the connecting legs (22) of the TO packages (2) to the printed circuit board (1);connecting (107) the holding down clamp (3) to a heat sink (4) or a structure (35) connected to the heat sink (4); andpressing (108) the TO package bodies (21) against an upper side (41) of the heat sink (4) through the holding down clamp (3).

18. The method of claim 17, wherein the holding down clamp (3) is connected to a clamp counterstructure (35) arranged at a bottom side (42) of the heat sink (4).

19. The method of claim 17 or 18, wherein the connecting legs (22) of the TO packages (2) are soldered both to the lower side (12) and to the upper side (11) of the printed circuit board (1).5 20. The method of any one of claims 17 to 19, wherein the semiconductor switches (2) arearranged in one row (A) or several parallel rows (A-D), wherein holding down clamps (3) are provided in accordance with the number of rows (A-D) of semiconductor switches (2), and wherein each holding down clamp (3) presses the semiconductor switches (2) of one row (A-D) against the upper side (41) of the heat sink (4).10

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