CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the national phase entry of international patent application no. PCT/EP2019/076506 filed Oct. 1, 2019 and claims the benefit of German patent application No. 10 2018 127 075.5, filed Oct. 30, 2018, the disclosures of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The subject matter relates to a high-current circuit, in particular a motor vehicle high-current circuit, in particular a high-current switch, a controlled high-current resistor and an automatic start-stop circuit.

BACKGROUND ART

The constant increase in the number of electrical components in modern vehicles causes an increasing energy demand and associated high amperages. Very high switching currents occur, which are switched with semiconductor switches, for example MOSFETs or IGBTs. Due to the high currents that are switched with these semiconductor switches, two challenges arise. On the one hand, the current-carrying capacity must be guaranteed by the circuit, which means that currents of up to several 100 A must be able to flow through the circuit. This high current-carrying capacity requires large conductor cross-sections, which usually cannot be realised on printed circuit boards. Complex high-current printed circuit boards with an electrically conductive substrate are known, but these are very expensive to manufacture and thus rather unsuitable for mass use. On the other hand, the high current flows result in considerable ohmic losses, whose Joule heat must be dissipated. The heat dissipation of conventional printed circuit boards is low, since their substrates are not conductive and thus also represent a poor thermal conductor.

For this reason, the subject matter was based on the object of providing a high-current circuit which, using conventional printed circuit boards, satisfies both the requirements for current-carrying capacity and the requirements for waste heat for applications with high currents, in particular in motor vehicles.

SUMMARY OF THE INVENTION

As mentioned at the beginning, the circuit is to be realised with a conventional printed circuit board. Such a printed circuit board is formed from a non-conductive substrate, a conductive layer applied to the substrate and an insulating layer applied to the conductive layer. The substrate may be a so-called prepreg. In particular, the substrate may be formed from a fibrous material and/or a synthetic resin. Substrates for printed circuit boards are well known. Any substrates known for printed circuit boards which are non-conductive can be used for the present application.

First, a conductive layer is applied to the substrate, which is, for example, a copper layer. In conventional printed circuit boards, this conductor layer is adapted by exposure and etching so that conductor tracks and contact pads are arranged on the printed circuit board. An insulation layer is applied to the conductor tracks etched in this way, whereby contact pads are excluded from the insulation. Also in the present printed circuit board, both conductor tracks and contact pads are provided.

In the present printed circuit board, contact pads that break through the insulation layer are arranged on both sides. These contact pads make contact with each other via conductive vias through the substrate of the printed circuit board. The vias are located directly in the area of the contact pads. The vias break through the substrate essentially vertically, so that the contact pads, which are connected to one another via vias, are arranged directly above one another in a normal projection onto the substrate.

To ensure a high current-carrying capacity while at the same time providing good thermal conduction, it is proposed that at least a first one of the contact pads is arranged on a first side of the printed circuit board and a first semiconductor switch is directly connected to at least a second one of the contact pads on a second side of the printed circuit board. The semiconductor switch is thus located directly on the second contact pad and an electrical connection between the first contact pad and the second contact pad is made via the vias arranged between the first and the second contact pad. This makes it possible to connect the semiconductor switch to the first contact pad via the second contact pad and the vias without the need for further conductor tracks. This means that the contact pads arranged on opposite sides of the PCB are directly connected via the vias and a current from a semiconductor switch can reach the first contact pad directly via the second contact pad and the vias without being routed via thin conductor tracks applied to the substrate.

This directness of the connection between the first side of the PCB and the second side of the PCB has the particular advantage that a very high current-carrying capacity is ensured, since the current does not have to be conducted via thin conductor layers, but can flow directly through the vias. In addition, the contacting of two contact pads via vias is a particularly simple method for the production of printed circuit boards that is suitable for mass production, so that the printed circuit boards can also be reliably produced in large quantities.

Furthermore, it is possible to apply a heat sink or a flat part directly on the contact pad and/or directly on the semiconductor switch.

According to an embodiment, it is proposed that the areas of the first and second contact pads are arranged one above the other on the two sides of the printed circuit board. Thus, in a normal projection onto the PCB, the two contact pads arranged on opposite sides of the PCB overlap each other. In particular, the size of the contact pads is substantially identical. The contact pads are larger than conventional contact pads in that they occupy areas that are a multiple, in particular by a factor of more than 10, preferably more than 50, larger than the areas of contact pins of the semiconductor switches, so that the contact pads have a high current-carrying capacity.

According to one embodiment, it is proposed that a flat part is directly connected to the first of the contact pads on the first side of the printed circuit board. The flat part can rest directly on the first contact pad and, in particular, be connected to the contact pad over its entire area. The contact pad on the first side of the printed circuit board can occupy an area that extends over the area of connection pins of a plurality of semiconductor switches. Thus, it is possible that on the second side of the PCB two or more semiconductor switches are electrically connected in parallel to each other via second contact pads to the first contact pad and the first and/or second contact pad is full-surface and has a single electrical potential.

It is also possible that the contact pad is metallically coated over its entire area, in particular with a tin layer. Thus, on the one hand, a current flow and, on the other hand, a heat transfer are possible over the entire contact pad. If the flat part is directly connected to the first contact pad and the first contact pad has a large surface area, very good heat transfer from the contact pad to the flat part is possible. The flat part can be applied directly to the first contact pad, in particular soldered. The flat part can be placed on the contact pad and connected to the contact pad by means of reflow soldering, for example. The contact pad lying in the area of the surface of the flat part can be full-surface, without interruption, so that heat transfer from the contact pad to the flat part is possibly high.

According to an embodiment, it is proposed that on the second side of the printed circuit board at least one contact pin of the semiconductor switch is directly connected to the first of the contact pads. A semiconductor switch may also be connected with all contact pins of a power terminal to the first contact pad. In this case, all contact pins can be at the same electrical potential and the contact pad can be the only surface connected to these contact pins. This also enables large-area heat dissipation and contacting with the contact pins of the semiconductor switch. The semiconductor switches may have two power terminals as well as one switching terminal. Power terminals are, for example, source and drain, and a switching terminal may be gate.

As explained above, one or more semiconductor switches may have a first power terminal directly connected to the first contact pad. On the second side of the PCB, there may further be a third contact pad which is connected to second contact pins of the semiconductor switch. It is possible that two semiconductor switches are connected in series with each other on the second side of the circuit board and that the series-connected semiconductor switches are directly connected via a third contact pad. The semiconductor switches can rest on the second side of the printed circuit board and on the one hand be arranged with contact pins of a power terminal on first contact pads and be connected with the corresponding contact pins of a power terminal on a third contact pad. The third contact pad creates an electrical short circuit between the two semiconductor switches or the contact pins of a power terminal. The entire current to be switched flows via this third contact pad.

Corresponding to the third contact pad, a fourth contact pad can be provided on the first side of the PCB. This contact pad may be insulated from the first contact pads. The fourth contact pad can be contacted with the third contact pad via vias. Thus, on the one hand, a current can flow via the fourth contact pad and, on the other hand, the fourth contact pad can be used for heat transfer.

The structure of the high-current circuit can, for example, be such that the semiconductor switches are arranged on the second side of the circuit board and the flat parts are arranged on the first side of the circuit board. For example, it is possible that a first flat part is connected to a first contact pad over the entire surface. This first contact pad can be electrically contacted with a second contact pad via vias.

At least a first semiconductor switch can be connected to the second contact pad with its power terminal. The corresponding second power terminal of the at least one first semiconductor switch can be connected to a third contact pad, which is electrically insulated from the second and the first contact pad.

A fourth contact pad can be arranged on the side of the printed circuit board opposite the third contact pad, which is connected to the third contact pad via vias. A flat part can be attached to the fourth contact pad over its entire surface, preferably like the first flat part on the first contact pad. A good heat dissipation can be realised via this flat part.

Starting from the third contact pad, at least one further semiconductor switch can be arranged as a mirror image of the at least one first semiconductor switch, whereby the at least one further semiconductor switch is initially arranged with its power terminal on the third contact pad and is arranged with its corresponding power terminal on a fifth contact pad.

A sixth contact pad can be arranged opposite the fifth contact pad corresponding to the first contact pad. The fifth and sixth contact pads can be formed corresponding to the first and second contact pads, in particular identically thereto. A flat part can again be arranged on the sixth contact pad, which is arranged like the first flat part on the first contact pad. The flat parts arranged on the first and sixth contact pad can be formed as a terminal lug.

The flat parts may be formed of copper, a copper alloy, aluminium or an aluminium alloy. It is also possible for the flat parts to be formed bimetallically, whereby the areas in contact with the contact pads are formed from a copper alloy and the terminal lugs projecting from the surface of the printed circuit board can be formed from an aluminium alloy. A mirror-inverted arrangement of copper alloy and aluminium alloy is also possible.

A sandwich-like structure in such a way that the printed circuit board is arranged between the semiconductor switches and the flat parts, with the semiconductor switches being arranged on one side of the printed circuit board and the flat parts on the other side of the printed circuit board, is also preferred.

According to an embodiment, it is also possible that on the first side of the PCB corresponding to the second side of the PCB, a second semiconductor switch is directly connected to the first contact pad. This is particularly possible if the semiconductor switches have their power terminals on their wide surfaces. The semiconductor switches are usually cuboid-shaped. Two opposite, wide surfaces can each be provided with a power terminal (source/drain). These power terminals can be arranged over a large area, in particular over the entire surface of the wide surfaces of the semiconductor switches. The wide surfaces of the semiconductor switches can be arranged over their entire surface on the contact pads and, in particular, soldered to them.

The printed circuit board is preferably sandwiched between two semiconductor switches. The contact pads are connected to each other via a plurality of vias. A current thus flows directly via the vias between the semiconductor switches and a conductor track is not necessary.

In the two variants described above, it should be noted that a switching terminal (gate) can be controlled via at least one separate contact pin of the semiconductor switch in each case. The gate contact can be controlled via a conductor track arranged on the printed circuit board. Only one switching current flows via the gate terminal, so that this can be routed via conductor tracks. The first to sixth contact pads are insulated from the gate terminal and the respective conductor track leading to the contact pin of the switching terminal of the semiconductor switch.

For good thermal conduction, it is proposed that the first and/or second semiconductor switch is directly connected to a flat part on a side facing away from the contact pads. The second side of the semiconductor switch is in particular also a wide surface on which a power terminal of the semiconductor switch is arranged. It is possible that one or both of the opposing semiconductor switches are each connected to a wide surface on one of the contact pads, respectively, and to the other wide surface with a flat part, respectively.

As explained, the contact pads are directly connected to each other via vias without any conductive tracks in between. This means that, according to one embodiment, the semiconductor switches are connected to each other exclusively via the vias. The semiconductor switches are arranged with their contact pins or contact surfaces of the power terminals directly on the contact pads, which are directly connected to each other via the vias. Thus, a current flow between the semiconductor switches takes place directly via the vias.

According to an embodiment, it is proposed that on the first side of the printed circuit board a contact pad has an area which is at least equal to the area of all terminals of the at least one semiconductor switch contacted on the second side of the printed circuit board. The at least one semiconductor switch on the second side of the printed circuit board may be contacted with two contact pads, wherein a first contact pad is provided for the contact pins of the power terminal of the semiconductor switch and a second contact pad, which is smaller for this purpose, is provided for the contact pin of the switching terminal. The contact pads of power terminals and switching terminals of several semiconductor switches can be arranged next to each other, insulated from each other, on the second side of the printed circuit board. Correspondingly, a full-surface contact pad can be located over the entire surface on the first side of the PCB. The contact pads of the power terminals on the second side of the printed circuit board are connected to the contact pad on the first side of the printed circuit board via a plurality of vias.

According to an embodiment, it is proposed that the flat part is connected to the at least one contact pad over the entire surface. A flat part may be arranged on the first contact pad, the fourth contact pad and/or the sixth contact pad. In this case, the flat part lies over the entire surface on the respective contact pad and is in particular soldered over the entire surface to the respective contact pad, so that the flat part enables current flow on the one hand and good heat transport on the other hand.

According to an embodiment, it is proposed that at least three contact pads insulated from each other are arranged on the first side of the printed circuit board. These may be the first contact pad, the fourth contact pad and the sixth contact pad. Corresponding contact pads, in particular second, third and fifth contact pads, are provided on the second side of the printed circuit board. The contact pads on the two sides of the printed circuit board are connected to each other exclusively via vias. The power terminals of the semiconductor switches are arranged on the contact pads of the second side of the PCB. Each of the contact pads on the first side of the printed circuit board is fully equipped with a flat part.

According to an embodiment, it is proposed that at least one contact pad for each of two power terminals is arranged on the second side of the printed circuit board for each semiconductor switch. The semiconductor switches can be connected on the input side, for example on a first power terminal with contact pads separated from one another, and contact pads can be provided in parallel for the switching terminals. This makes it possible to lead switching terminals to contact pins that are directly adjacent to the contact pins of the power terminals of the semiconductor switch.

On the other side of the semiconductor switch, where only power terminals are routed to contact pins, all contact pins can rest on a full-surface contact pad. It is thus possible for a single contact pad, in particular the third contact pad, to connect a plurality of power terminals of semiconductor switches to one another. The contact pad is full-surface and uninterrupted.

In order to enable good current transport, in particular to ensure the current carrying capacity of the circuit, a plurality of vias per contact pad is provided. The number of vias per contact pad can exceed 10, in particular also 30. Thus, it is possible that 40-50 vias per contact pad are provided to allow a sufficiently high current flow.

According to an embodiment, it is proposed that at least one of the flat parts is led out of the surface of the printed circuit board and forms a connection lug for a power conductor. In a normal projection, i.e. in a top view of the printed circuit board, the flat part may be led out of the surface of the printed circuit board, thus enabling contacting with a terminal lug in a particularly simple manner.

According to an embodiment, it is proposed that the conductor layer between two edges of the printed circuit board is completely cut through and divides the printed circuit board into two areas, wherein a high-current circuit according to one of the preceding claims is arranged in a first area and a logic circuit is arranged in a second area. Thus, it is possible to accommodate both a power circuit and a logic circuit on a single printed circuit board. By separating the conductive layer, there is no electrically conductive connection between these two areas of the printed circuit board. As a result, heat transfer from the first area to the second area is severely impeded because the substrate of the PCB is a poor conductor of heat. On the one hand, this makes it possible to load the PCB in the area of the high-current circuit with currents that lead to temperatures that are unsuitable for logic devices. For example, the high-current circuit can heat up to over 80° C. without negatively affecting logic components on the other side, since a thermal decoupling of the two areas of the PCB is ensured by separating the conductor layer.

