Electronic circuit and method of manufacturing the same, and improved active power semiconductor for incorporation in the electronic circuit and method of manufacturing the same
Patent Information
- Application Number
- EP2023712473
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-03-17
- Filing Date
- 2023-03-15
- Publication Date
- 2025-01-22
AI Technical Summary
Existing electronic circuits face challenges in achieving high efficiency and low parasitic capacitances while requiring minimal space, especially at high frequencies and power levels, due to the need for extensive isolation and shielding between control and power circuits.
The solution involves separating the power and control circuits onto distinct circuit boards, with the power circuit on a metal core board for efficient heat dissipation and current density, and using improved active power semiconductors with bent control connections to minimize parasitic effects and reduce space requirements.
This configuration achieves high efficiency, low parasitic capacitances, and effective isolation, enabling high-frequency switching of high electrical power with reduced space and parasitic effects, making it suitable for high-performance applications.
Smart Images
Figure 1.1
Abstract
Description
[0001] Electronic circuit and method for its manufacture, as well as improved active power semiconductor for incorporation into the electronic circuit and method for its manufacture
[0002] The invention relates to an electronic circuit and a method for its production according to the preamble of claim 1 and claim 8, respectively, as well as to an improved active power semiconductor for incorporation into the electronic circuit and a method for its production according to the preamble of claim 5 and claim 6, respectively.
[0003] Innovative transistor modules are available on the market, primarily containing SiCFETs in various topologies (e.g., as half- or full-bridge circuits). The transistor modules are designed for direct PCB mounting and feature contact pins. They offer high performance for their size, with a current-carrying capacity of approximately 200 A per transistor functional element. The bottom of the module is mounted directly onto a heat sink to dissipate power loss. A printed circuit board (PCB) is attached to the top, which simultaneously handles the wiring of the power and control circuits. The transistor modules, with their contact pins, are designed for press-fit or soldered connections to the PCB. The power range of these innovative modules, at least based on the semiconductor specifications, enables applications up to 100 kW.
[0004] Due to the ever-increasing switching frequencies made possible by modern semiconductors, ever more comprehensive measures must be taken to isolate the control circuits so that they remain largely unaffected by the high-frequency switched power. This can be achieved to a certain extent through optimized conductor paths on the multilayer circuit boards used. Additional insulation measures are also possible. However, the measures mentioned require a lot of space. Furthermore, the maximum power stated above can hardly be increased by these measures. Instead of using the transistor modules described above, such circuits for high power can also be implemented using discrete power semiconductors. Suitable active power semiconductors in a package for THD soldering technology (through-hole technology) are now available on the market.These components even have a Kelvin terminal for control. This means that an additional ground connection is provided as an additional pin (Kelvin terminal) on the semiconductor component as a reference potential for the gate terminal. This eliminates ground loops between the control and power circuits. The component therefore no longer has three, but four, connection pins. This allows the control circuit to be easily separated from the power circuit, although a galvanic connection still exists between the two. Since several discrete power semiconductors must be used to achieve the same performance class as the transistor modules described above, a relatively large-area design is necessary. A lot of space is also required to adequately shield the control circuit from the power circuit.This large-scale structure is not only a space problem, but also creates significant parasitic effects.
[0005] The object of the invention was therefore to create an electronic circuit, a method for its manufacture, an improved active power semiconductor for incorporation into the electronic circuit, and a method for its manufacture. The novel electronic circuit should exhibit the highest possible efficiency and low parasitic capacitances while also requiring minimal space. Nevertheless, the electronic circuit should also be usable at high frequencies and for high power levels.
[0006] The object is achieved according to the invention by an electronic circuit and a method for its production according to claim 1 and claim 9, respectively, as well as an improved active power semiconductor for incorporation into the electronic circuit and a method for its production according to claim 6 and claim 7, respectively. Further details and advantages of the invention emerge from the subclaims.
[0007] Because the power circuit is arranged on the first circuit board and the control circuit on the second circuit board, and because the power connections of the at least one active power semiconductor are soldered to the power circuit on the first circuit board and the control connection(s) are soldered to the control circuit on the second circuit board, excellent spatial separation of the control circuit and power circuit is possible while keeping the electronic circuit very small. The control circuit comprises the actual control for switching the at least one active power semiconductor, as well as the driver(s) for it. The entire control circuit, which is operated at low voltage, is therefore arranged on a separate circuit board and is therefore not disturbed by a power circuit operated at a high switching frequency.Additional shielding measures are normally not necessary because the power circuit is located on a separate circuit board. Nevertheless, the control circuit and the power circuit are connected via the terminals of the at least one active power semiconductor over very short current-carrying paths. The inventive design of the electronic circuit ensures high efficiency and has only low parasitic capacitances. By arranging the control circuit on its own circuit board, the influence of high-frequency oscillations on the control circuit can be avoided. Potential feedback to the control circuit is also minimized. Parasitic effects are greatly reduced by the shortest possible connections within the gate control circuit. The electronic circuit is therefore ideally suited for high-frequency switching of high electrical power.
[0008] The term "control circuit" here refers specifically to the drivers for the power semiconductors. However, additional control elements operating at low voltage can be located on the second circuit board. It is also possible to outsource additional control elements to a third circuit board.
[0009] In order to be able to realize the shortest possible electrical connections between all components that interact directly with the power circuit, the intermediate circuit capacitors for the power circuit are also arranged on the first circuit board according to the invention.
[0010] State-of-the-art electronic circuits typically utilize multilayer printed circuit boards. To switch high power levels, very wide conductor tracks must be provided. Under certain circumstances, additional copper structures may even be necessary to provide the required conductor cross-sections. Since the power circuit in the inventive electronic circuit is located on a different circuit board than the control circuit, the first circuit board on which the power circuit is located can be designed as a metal-core circuit board. This makes it easy to achieve the necessary current-carrying capacity, as a higher current density within the conductor tracks can be utilized due to improved heat dissipation.
[0011] Despite the high efficiency of the electronic circuit according to the invention, a not inconsiderable amount of heat is generated by the flow and switching losses of the at least one active power semiconductor. In order to dissipate this heat effectively, the first circuit board is thermally conductively connected to a heat sink on the side opposite the at least one active power semiconductor. The connection is particularly advantageously made using solder, but a connection using a thermal adhesive is also possible. The heat sink can be either a heat sink in which the heat is dissipated via a coolant inside the heat sink, for example a cooling fluid passed through the heat sink, or a heat sink that is cooled from the outside, for example with air.
[0012] When assembling the first circuit board with multiple active power semiconductors and arranging the components accordingly on the first circuit board, it might be possible to connect the second circuit board with the control circuit to the first circuit board only via the control terminals of the active power semiconductors, which are bent upwards and soldered into the mounting holes. However, it is advantageous to provide spacers between the first circuit board and the second circuit board. This not only has advantages during manufacturing but can also prevent vibrations from being transmitted from the power circuit to the control circuit during operation.
[0013] To construct the electronic circuit according to the invention, an improved active power semiconductor is required. In this improved active power semiconductor, several power terminals are aligned toward its base surface, with which it rests on a circuit board, and the control terminal(s) are aligned in the opposite direction. This allows an active power semiconductor to be soldered directly to two circuit boards. This also makes it possible to separate the power circuit and control circuit onto two independent circuit boards without having to accept long current paths.
[0014] Active power semiconductors in an SMD (Surface Mounted Device) housing are a mass product that is launched on the market in such a way that all connections can be soldered to a circuit board using an SMD process. In order to be able to implement the electronic circuit according to the invention, improved active power semiconductors must therefore be manufactured from commercially available active power semiconductors. According to the invention, an active power semiconductor with an SMD housing, which is intended for soldering to a circuit board and has one or more control connections aligned in the direction of the circuit board to be soldered and several power connections also aligned in the direction of the circuit board to be soldered, is fed to a bending device and the control connection or connections aligned in the direction of the circuit board to be soldered are bent in the opposite direction.
[0015] To achieve this specific terminal alignment, the control terminal(s) can be bent in the desired direction as described above. However, it is also possible to shorten the control terminal(s) to a short, straight section protruding from the housing and weld a piece of conductive material of the desired length and orientation to the shortened control terminal(s).
[0016] The terminals of an active power semiconductor are very thin and are primarily held in place by the housing. To prevent the housing from being damaged (e.g., by hairline cracks) or even breaking and thus being destroyed during the bending process, the control terminals to be bent are clamped close to the housing.
[0017] To produce the electronic circuit according to the invention, at least one improved active power semiconductor, as described above, is produced as described above. Furthermore, a first circuit board is populated with electronic components for the power circuit, spacers for a second circuit board, and at least one improved active power semiconductor. A second circuit board is provided with one or more receiving holes for the control terminal(s) of the at least one improved active power semiconductor and is populated with electronic components for the control circuit.
[0018] In a first embodiment, the second circuit board is then placed onto the first circuit board. In the next step, both circuit boards are soldered together in a single operation. Advantageously, the step of producing the at least one improved active semiconductor is performed first. The assembly of the two circuit boards can then be performed in parallel. However, serial processing of all steps is also possible.
[0019] If the PCBs are to be assembled in a pick-and-place machine, it is advisable to place both PCBs in a common holder, eliminating the need to adjust the pick-and-place machine to accommodate different PCB widths. Both PCBs can be assembled on the holder in a single pass.
[0020] The mounting holes in the second circuit board are filled with solder paste, for example, before the soldering process, so that a good electrical transition can be created between the at least one control terminal of the at least one improved active semiconductor and the control circuit during the soldering process. However, it must be prevented that the solder paste - when heated during the soldering process - runs downwards out of the mounting holes. Likewise, it must be prevented that solder running down the control terminals causes a short circuit between the control terminals. Therefore, the control terminal(s) of the at least one improved active power semiconductor to be soldered to the second circuit board are provided with a safeguard against solder leakage from the mounting holes of the second circuit board during the soldering process.This can be advantageously achieved by applying a high-temperature-resistant adhesive between the control terminals or by attaching silicone washers to the free ends of the control terminals. In a second embodiment, both the first and second circuit boards are soldered individually after assembly. In this way, complete first and second circuit boards can be manufactured in advance, stored, and assembled only when needed.
[0021] Advantageously, the first circuit board is thermally connected to a heat sink, in particular by soldering. The timing of joining the first circuit board and heat sink depends fundamentally on the manufacturing process.
[0022] The electronic circuit according to the invention can advantageously be manufactured entirely in a suitably equipped assembly machine. However, it is also possible to use handling robots for individual or all production steps. The second circuit board can also be placed on the first circuit board either with a handling robot or with the assembly machine. When using one or more handling robots for assembling the circuit boards, the heat sink can be coupled to the first circuit board prior to assembly.
[0023] Certain pick-and-place machines have a limit on the height for passing circuit boards. With a higher heat sink, this can result in the pick-and-place machine's throughput height no longer being sufficient for a circuit board that is already coupled to the heat sink. In this case, it makes sense to add the heat sink after assembly. For example, the two assembled circuit boards can still be joined very precisely in the machine. The two circuit boards can then be inserted into another holder that already contains the heat sink, so that the joining of the circuit boards with the heat sink only takes place after the pick-and-place machine.
[0024] When the two circuit boards are completed (soldered) separately, it is particularly advantageous if the second circuit board is placed on the first circuit board and the control terminals of the at least one active power semiconductor on the first circuit board are soldered to the second circuit board using a handling robot. In this way, only one automatic soldering process is required after the circuit boards have been connected. Further details and advantages of the invention will become apparent from the description of an exemplary embodiment, which is explained in detail with reference to the drawing.
[0025] It shows:
[0026] Fig. 1 shows an improved active power semiconductor according to the invention in side view,
[0027] Fig. 2 the component from Fig. 1 in front view,
[0028] Fig. 3 the upwardly bent electrical connections of the component from Figures 1 and 2,
[0029] Fig. 4 is a schematic side view of the electronic circuit according to the invention,
[0030] Fig. 5 is a schematic representation of the bending process in a bending device according to a first embodiment,
[0031] Fig. 6 a part of the bending device according to Fig. 5,
[0032] Fig. 7 shows part of a bending device according to a second embodiment,
[0033] Fig. 8 is a flow chart for the production of the electronic
[0034] Circuit and
[0035] Fig. 9 Circuit diagram for a SiC-MOS-FET component used in the circuit according to Fig. 4.
[0036] Figures 1 and 2 show an example of a SiC MOSFET in an SMD package with seven connection pins and drain terminal 2 as the active power semiconductor 1. Pin 3 serves as the gate terminal, pin 4 as the driver-source terminal, and the five pins 5 are designed as power-source terminals (see also the circuit diagram in Fig. 9). Both gate terminal 3 and driver-source terminal 4, which are both to be connected to the low-power control and driver circuit, are bent upward.
[0037] A SiC MOSFET is mentioned here only as an example. However, it should be emphasized that the invention naturally also applies to other active power semiconductors in an SMD package with connection pins protruding from the package. Even active power semiconductors in other packages, such as GaNFETs, can be used. For such components, where all connections are usually designed as solder pads facing downwards, modifications must be made so that the connections for the control and driver circuits are routed upwards and can thus be connected to an upper circuit board (see Fig. 4) via a short path.
[0038] A section of Fig. 2, which shows an enlarged view of only the two upwardly bent pins 3 and 4, is shown in Fig. 3. An elastic adhesive 6 is inserted between the two pins 3 and 4. This adhesive 6 is intended to prevent the liquefied solder from running between pins 3 and 4 from the mounting holes 10 of an upper circuit board 9 with the control and driver circuit, which is mounted above the active power semiconductor 1 or above the power semiconductors 1, during the soldering process, and thus creating a short circuit or being missing for a proper soldering joint in the mounting holes 10. The adhesive 6 can be applied using a handling robot directly after the bending process.
[0039] Fig. 3 illustrates another possibility, which is also intended to prevent liquid solder from flowing out of the mounting holes 10 of the upper circuit board 9: for this purpose, a silicone washer 7 can be placed on each of the upwardly bent pins 3 and 4, also using a handling robot. Any openings in the silicone washer 7 must be narrow enough that the silicone washer 7 tightly encloses the pins and is held securely in place. They may only be slightly displaced downward by the circuit board 9 when the upper circuit board 9 is placed in place, so that the lower openings of the mounting holes 10 are securely closed.
[0040] Fig. 4 shows an electronic circuit in which four active power semiconductors 1 are connected in parallel. Directly behind the visible power semiconductors 1, four additional power semiconductors can be arranged, also connected in parallel. These two legs can then be connected in series. This arrangement easily switches power levels above 50 kW. It is ideally suited for use in high-power voltage converters. For example, if three such legs are connected together, a frequency converter circuit for controlling the speed of electric motors up to 200 kW can be realized.
[0041] The lower circuit board 8 is mounted on a heat sink 11, which has a coolant inlet 12 and a coolant outlet 13. Depending on the geometry of the circuit design, the coolant channels 12 and 13 can run perpendicular to the direction shown in Fig. 4. In any case, the heat sink 11 is designed to ensure the best possible cooling of the active power semiconductors 1.
[0042] To further increase performance, an additional lower circuit board can be mounted on the heat sink 11 (not shown here) opposite the lower circuit board 8 shown. The heat sink 12 is then designed to absorb the waste heat from both lower circuit boards and dissipate it via the coolant.
[0043] In the illustrated embodiment, four active power semiconductors are connected in parallel on the lower circuit board 8 and soldered there to their power source terminals 5 and drain terminals 2. The upwardly bent pins 3 and 4 (the gate terminal and the driver source terminal) are soldered into the mounting holes 10 of the upper circuit board 9. To stabilize the upper circuit board 9, it is connected to the lower circuit board 8 via spacers 11. The lower circuit board 8 houses exclusively the power electronics, while the upper circuit board 9 only houses the control and driver circuitry. Therefore, only the lower circuit board 8 requires active cooling.
[0044] The bending process for the driver source terminal 3 and the gate terminal 4 will now be explained using Figures 5 to 7. In principle, the assembly of the lower circuit board 8 and the upper circuit board 9 can be carried out using a handling robot or an automatic placement machine. When using an automatic placement machine, the bending device is advantageously integrated into the machine.
[0045] The upward bending of pins 3 and 4 (driver source connection and gate connection) is preferably carried out immediately after removing the active power semiconductor 1 from the packaging or from a magazine. To avoid damage, mechanical stress must be prevented from being introduced into the housing of the active power semiconductor 1 during the bending process. An upper clamping die 15 and a lower clamping die 16 are provided for this purpose. These two clamping dies 15 and 16, which are moved toward pins 3 and 4 from above and below, respectively, clamp the two pins and thus fix them in place.
[0046] In a first embodiment, the upper clamping punch 15 has a rectangular cross-section. One edge (bottom right in the drawing) is provided with a bending radius (not shown) to prevent the two pins 3 and 4 from tearing during bending, which could potentially cause them to become unstable or even break. The clamping position with the clamping punches 15 and 16 moved toward the pins 3 and 4 is shown in Fig. 5a. The bending punch, which in this embodiment also has a rectangular cross-section, is located below the pins 3 and 4 in its rest position.
[0047] To perform the bend, the bending punch 17 is now moved upwards, as shown in Fig. 5b. Pins 3 and 4 are bent over the edge with the bending radius of the upper clamping punch 15 and pressed against the straight front surface of the upper clamping punch 15, which in the drawing is located behind the right vertical edge of the upper clamping punch 15. The bending punch 17 acts only on pins 3 and 4, while the remaining pins 5 (power source connections) are not affected by the bending process and remain in their original position.
[0048] Fig. 5C shows a position corresponding to the position shown in Fig. 5A, in which the bending punch 17 is already in its rest position below the original position of the pins. In contrast to Fig. 5A, however, pins 3 and 4 are already in their upwardly bent position.
[0049] In order to insert the two pins 3 and 4 into the two mounting holes 10 when placing the upper circuit board 9 and soldering them there, the distance between the two upwardly bent pins 3 and 4 is too small. Therefore, the two pins must be bent apart in a V-shape. This process is shown in Figures 5d to 5f. The forming die 18 with the forming punch 19 is provided for this purpose. These components are explained in more detail in Figure 6.
[0050] The forming die 18 has a V-shaped die recess 20. The forming punch 19 is shaped to fit the die recess 20. Its thickness corresponds to the depth of the die recess 20. The forming punch 19 is approximately pointed on its underside, ensuring that it can penetrate between the two free ends of the parallel, upwardly bent pins 3 and 4.
[0051] Fig. 5d now shows a position of the bending device in which the forming die 18, together with the forming punch 19 movable therein, has been moved toward the upper clamping punch 15. The upwardly bent pins 3 and 4 are now located within the die recess 20 and are therefore not visible in Fig. 5d.
[0052] As shown in Fig. 5e, the forming punch 19 is now moved downwards into the position shown in Fig. 6b. The lower tip of the forming punch 19 forces itself between the free ends of the two pins 3 and 4 and presses these outwards against the side walls of the die recess 20. If the forming punch 19 is now moved upwards again and the forming die 18 is returned to its rest position (see Figures 5a, 5b, 5c, 5f), the pins 3 and 4 are bent upwards and run in such a way that the distance between the two pins is greatest at the level of their free ends and is sufficient to place the upper circuit board 9 on top and to insert the pins into the two receiving holes 10. The two receiving holes 10 are spaced far enough apart from each other to enable problem-free soldering without bridging between the receiving holes 10.
[0053] Fig. 5f shows the rest position of the bending device, in which the upper clamping die 15 and the lower clamping die 16 are moved apart again, the fully bent power semiconductor 1 is removed, and the bending device can be loaded with a new power semiconductor. The following describes, by way of example, another possibility for bending pins 3 and 4 into the required position. The forming die 18 with the forming die 19 shown in Fig. 5 is not required. Instead, a modified upper clamping die 15a and a modified bending die 17a must be used.
[0054] The corresponding components are shown in Fig. 7, with Fig. 7a showing a front view of the upper clamping punch 15a and Fig. 7b showing a top view of the upper clamping punch 15a and the bending punch 17a. It can be seen that the upper clamping punch 15a has a V-shaped straight surface 21 in the middle on its front side. Outside of this straight surface 21 there are two angled surfaces 22 which have a small angle of less than 10° to the straight surface 21. On the lower edge of these angled surfaces 22 there is again a bending radius which also runs at the aforementioned angle to the lower edge of the straight surface 21. The straight surface 21 merges into the respective angled surface 22 via a connecting bevel 23.
[0055] The corresponding side of the bending punch 17a is roof-shaped. The roof slope is adapted to the angled surfaces 22 of the upper clamping punch 15a.
[0056] If the bending punch 17a is now moved upwards as shown in Fig. 5b, pins 3 and 4 are bent not along a straight edge as in the first described embodiment, but along an angled edge. In this case, pins 3 and 4 already assume the V-shaped position, in which the free ends are spaced further apart than the ends fixed in the housing. The connecting bevels 23 of the upper clamping punch 15a serve as a guide, allowing a precisely defined position to be achieved.
[0057] The method according to the invention will now be described with reference to Fig. 8. The method is divided into three process strands:
[0058] • In the first process chain with process steps 25 to 27, the lower circuit board 8 is prepared with the power circuit, • In the second process chain with process steps 28 to 30, the active power semiconductors 1 are prepared for assembly of the lower circuit board 8 and
[0059] • In the third process strand with process steps 32 to 34, the upper circuit board 9 with the control and driver circuit is prepared.
[0060] In the first process step 25 of the first process line, a metal-core circuit board is prepared for the assembly of electronic components on its top side and for the mounting of a heat sink on its bottom side. The circuit board 8 is advantageously prepared for assembly with SMD components. The solder paste is then applied accordingly. Since these are known procedures, these substeps need not be described in detail. The underside of the circuit board 8 is advantageously treated only with flux.
[0061] In process step 26, the heat sink 12 is placed on the underside of the prepared metal-core circuit board. For a larger heat sink, alignment pins or guide grooves can also be provided to hold the heat sink in position until the soldering process. To ensure a secure connection with good thermal transfer between the lower metal-core circuit board 8 and the heat sink 12, the heat sink 12 can also be treated with flux and a suitable solder foil applied to the heat sink.
[0062] If the circuit boards are to be assembled in an assembly machine, it is advisable to bring the heat sink 12 together with the lower circuit board 8 only after the two circuit boards have been assembled and stacked on top of each other, since the height of the assembly machine may not be sufficient to accommodate the lower circuit board together with the heat sink.
[0063] In the next process step 27, the spacers 11 are then attached, via which the connection to the upper circuit board 9 will later be established. Advantageously, the spacers 11 are also connected to the lower circuit board 8 using solder paste and then soldered to the lower circuit board 8 in the subsequent soldering process. In the parallel second process step, the active power semiconductors 1 are prepared so that they can later be incorporated into the assembly of the lower circuit board 8. For this purpose, the power semiconductors 1 are removed in process step 28 either directly from the packaging or from a magazine and inserted into a bending device.
[0064] In process step 29, the gate terminal 3 and the driver-source terminal 4 are bent upwards as already described above in the text.
[0065] In process step 30, the space between the two upwardly bent pins 3 and 4 is then filled either with an elastic adhesive or with covering material 6, or silicone discs 7 are placed on the free ends of the upwardly bent pins 3 and 4. When applying the adhesive, care must be taken to ensure that the free ends of the upwardly bent pins 3 and 4 that are still to be soldered remain free of adhesive. The improved active power semiconductors 1 prepared in this way are temporarily stored in a memory until the lower circuit board 8 is populated.
[0066] In a further step not shown in the drawing, it is advisable to apply ESD (electrostatic discharge) protection. For this purpose, a piece of self-adhesive copper tape is used to electrically connect the gate terminal 3 and the driver-source terminal 4 of each enhanced active power semiconductor.
[0067] The process steps 28 to 30 of the second process strand are repeated until as many prepared power semiconductors 1 are present in the buffer as are required for the assembly of the lower circuit board 8.
[0068] In the third process step, in process step 32, the upper circuit board 9 is provided with the mounting holes 10 for the upwardly bent pins 3 and 4 of the prepared power semiconductors 1. The upper circuit board 9 is also a circuit board that is populated with SMD components. In process step 33, the solder paste is now also applied to the upper circuit board 9. In the process, the mounting holes 10 for the upwardly bent pins 3 and 4 of the improved active power semiconductors 1 must also be filled with solder paste (according to a known THR process). Likewise, the areas on the underside of the upper circuit board 9, where the spacers 11 will later be attached, are provided with solder paste. Alternatively, the spacers 11 can also be coated with solder paste on their upper side.
[0069] After these preparations, both circuit boards 8 and 9 can be populated. The assembly can be performed in a placement machine or with a handling robot. In the first case, the bending device can be integrated directly into the placement machine. When using a handling robot, it is advisable to place both the lower circuit board 8 and the upper circuit board 9 on a holding device within the working area of the handling robot. The assembly can then be performed sequentially or in parallel by at least two handling robots.
[0070] When using a placement machine, the circuit boards 8 and 9 are also inserted into a common holder and fed together on this holder to the placement machine.
[0071] In process step 31, the electronic components for the power circuit are placed on the lower circuit board 8. This includes the already prepared active power semiconductors 1, which are stored in the buffer. Furthermore, a connection terminal is included, which must be accessible even after the upper circuit board 9 has been placed on the board, so that the necessary cables can be connected even after the soldering process.
[0072] In process step 34, the upper circuit board 9 is populated by attaching all components required for the control and driver circuitry. When using an automatic placement machine, process steps 31 and 34 are advantageously performed in parallel within the placement machine.
[0073] After both circuit boards 8 and 9 have been populated with the electronic components, both circuit boards 8 and 9 are connected to each other in process step 35. This requires precise positioning of the upper circuit board 9 above the lower circuit board 8. After positioning, either the upper circuit board 9 is lowered or the lower circuit board 8 is raised. The upwardly bent pins 3 and 4 of the power semiconductors 1 penetrate into the receiving holes 10 in the upper circuit board 9, which are filled with solder paste. The circuit boards 8 and 9 are brought together until the upper circuit board 9 rests on the spacers 11. Fastening with screws is possible, but also gluing with a high-temperature-resistant adhesive. Advantageously, the upper circuit board 9 is also soldered to the spacers 11.When using a placement machine, this process step is advantageously also carried out in the placement machine.
[0074] The adhesive 6 between the upwardly bent pins 3 and 4 of the power semiconductors 1 or the silicone discs 7 attached to the free ends now seal the mounting holes 10 in the upper circuit board 9 at the bottom. This prevents solder from leaking out of the mounting holes 10 during the soldering process.
[0075] The soldering process can now be performed in process step 36. During this soldering process, both the components of the upper circuit board 9 and the components of the lower circuit board 8 and the heat sink 12 are soldered simultaneously. This ensures the lowest possible thermal load on the electronic components.
[0076] In an alternative method, not shown in the drawing, the lower 8 and the upper circuit board 9 are each individually assembled and soldered.
[0077] The heat sink 12 can then be connected to the lower, fully soldered circuit board 8. This process is advantageously carried out using low-temperature solder in a vacuum chamber. With proper design of the process, it is possible to perform the soldering process without flux, thus creating a composite of the heat sink 12 and the lower circuit board 8 that ensures very uniform heat transfer from the lower circuit board 8 to the heat sink 12 across the connection surface. It is of course also possible to connect the lower circuit board(s) to the heat sink 12 in another way that ensures good heat transfer. One example of this is bonding with a thermal adhesive.
[0078] Ideally, two lower circuit boards are soldered to a heat sink 12, so that the heat sink 12 is located between the two lower circuit boards. In this way, two lower circuit boards can be cooled with just one heat sink 12.
[0079] Now, the lower circuit board 8 with the power circuit and intermediate capacitors can be tested. For this purpose, the lower circuit board 8 is energized, and the thermal transitions of the solder joints are monitored with a thermal imaging camera.
[0080] If everything is in order, the upper circuit board 9 can be mounted on the lower circuit board 8, and the gate terminal 3 and the driver-source terminal 4 of the at least one improved active power semiconductor 1 can be soldered to the upper circuit board 9. This is advantageously done with the aid of a handling robot. If a heat sink 12 is soldered to two lower circuit boards, two upper circuit boards are also mounted to this module.
[0081] A finished module then consists of a heat sink 12, two lower circuit boards soldered to two opposite surfaces of the heat sink 12, and an upper circuit board mounted on top of each lower circuit board. By stringing together several such modules, enormous power density can be achieved.
[0082] If a self-adhesive copper foil was used for ESD protection of the improved active power semiconductors 1—as described above—this must be removed before mounting the upper circuit board 9 on the lower circuit board 8. List of reference symbols:
[0083] 1 active power semiconductor
[0084] 2 Drain connection
[0085] 3 Gate connection
[0086] 4 Driver source connector
[0087] 5 power source connections
[0088] 6 glue
[0089] 7 silicone discs
[0090] 8 lower circuit board
[0091] 9 upper circuit board
[0092] 10 mounting holes
[0093] 11 spacers
[0094] 12 heat sinks
[0095] 13 Coolant inlet
[0096] 14 Coolant drain
[0097] 15 upper clamping stamp
[0098] 16 lower clamping stamp
[0099] 17 bending punches
[0100] 18 forming die
[0101] 19 forming stamps
[0102] 20 die recess
[0103] 21 straight surface
[0104] 22 angled surface
[0105] 23 Connecting slope
[0106] 24 Lower edge of the angled surface with bending radius
[0107] 25 Preparing the metal core circuit board
[0108] 26 Attaching the heatsink
[0109] 27 Attaching the spacers
[0110] 28 Inserting the power semiconductors into the bending device
[0111] 29 Bending process 30 Attaching a safety device to prevent solder from flowing out
[0112] 31 Assembling the metal core circuit board
[0113] 32 Drilling the mounting holes in the upper circuit board
[0114] 33 Preparing the upper circuit board 34 Assembling the upper circuit board
[0115] 35 Joining the two circuit boards
[0116] 36 Soldering the electronic circuit
Claims
Patent claims 1. Electronic circuit comprising a first printed circuit board (8) and at least one second printed circuit board (9) arranged in parallel, comprising at least one active power semiconductor (1) on the first printed circuit board (8) having one or more control terminals (3, 4) and several power terminals (2, 5), comprising a control circuit for controlling the at least one active power semiconductor (1) and a power circuit, wherein the control terminal(s) (3, 4) are connected to the control circuit and the power terminals (2, 5) are connected to the power circuit, characterized in that the power circuit is arranged on the first printed circuit board (8) and the control circuit is arranged on the second printed circuit board (9) and that the power terminals (2, 5) of the at least one active power semiconductor (1) are soldered to the power circuit on the first printed circuit board (8) and the control terminal(s) (3, 4) are soldered to the control circuit on the second printed circuit board (9).
2. Electronic circuit according to claim 1, characterized in that intermediate circuit capacitors for the power circuit are arranged on the first printed circuit board (8).
3. Electronic circuit according to one of claims 1 to 2, characterized in that the first circuit board (8) is designed as a metal core circuit board.
4. Electronic circuit according to one of claims 1 to 3, characterized in that the first circuit board (8) is thermally connected to a heat sink (12) on the side opposite the at least one active power semiconductor (1).
5. Electronic circuit according to one of claims 1 to 4, characterized in that spacers (11) are provided between the first printed circuit board (8) and the second printed circuit board (9).
6. Improved active power semiconductor (1) with one or more control terminals (3, 4) and several power terminals (2, 5) for installation in an electronic circuit according to one of claims 1 to 5, characterized in that several power terminals (5) are oriented in the direction of its base surface with which it sits on a printed circuit board and the control terminal(s) (3, 4) are oriented in the opposite direction.
7. Method for producing an improved active power semiconductor according to claim 6, characterized in that an active power semiconductor (1) with an SMD package, which is intended for soldering to a printed circuit board and has one or more control terminals (3, 4) oriented towards the printed circuit board to be soldered and several power terminals (5) also oriented towards the printed circuit board to be soldered, is fed to a bending device and the control terminal(s) (3, 4) oriented towards the printed circuit board to be soldered are bent in the opposite direction (29).
8. Method according to claim 7, characterized in that during the bending process (29) the control connections (3, 4) to be bent are clamped close to the housing (15, 16).
9. Method for manufacturing an electronic circuit according to one of claims 1 to 5, characterized in that at least one improved active power semiconductor according to claim 6 is manufactured in a method according to one of claims 7 to 8 (29), a first printed circuit board (8) is equipped with electronic components for the power circuit, with spacers (11) for a second printed circuit board (9) and with at least one improved active power semiconductor (1) (26, 27, 31), that a second printed circuit board (9) is provided with one or more receiving holes (11) for the control connections (3 4) of the at least one improved active power semiconductor (1) a second printed circuit board (8) is provided with an improved active power semiconductor (1) (32) and is populated with electronic components for the control circuit (34). Method according to claim 9, characterized in that the second printed circuit board (9) is placed on the first printed circuit board (8) (35) and that both printed circuit boards (8, 9) are soldered together in one operation (36). Method according to claim 10, characterized in that the control connections (3, 4) of the at least one active power semiconductor (1) to be soldered to the second printed circuit board (9) are provided with a safeguard (6, 7) against solder leakage from the receiving holes (11) of the second printed circuit board (9) during the soldering process (30). Method according to claim 9, characterized in that both the first printed circuit board (8) and the second printed circuit board (9) are soldered individually after assembly.A method according to at least one of claims 9 to 10, characterized in that the first printed circuit board (8) is thermally connected to a heat sink (12). A method according to one of claims 12 to 13, characterized in that the second printed circuit board (9) is placed on the first printed circuit board (8) and the control connections (3, 4) of the at least one active power semiconductor (1) on the first printed circuit board (8) are soldered to the second printed circuit board (9) using a handling robot.