The invention relates to a printed circuit board having a layer structure, which comprises a transformer for galvanic isolation between individual electric circuits.
US 2011/0095620 A1=DE 10 2007 034 750 A1 discloses an improved galvanic isolator with an inductive transducer in a layer structure. On the upper and lower surfaces of a substrate plate which forms a barrier layer having a sufficient thickness and sufficient insulation characteristics, conductive traces are provided to define coil windings which are protected by insulating cover layers which partially have feeding conductive traces extending thereon which, in a first embodiment, are connected to a transmitter chip or a receiver chip through vias. The vias extend through the insulating cover layers and partly through the substrate plate as well. The coil windings form the inductive transducer which, in a second embodiment, is connected to the transmitter chip and the receiver chip by wire connections. Thus, the chips with the electrical or electronic components are arranged outside the galvanic isolator.
A broadband radio-frequency transformer having a layer structure is known from U.S. Pat. No. 5,015,972, wherein primary and secondary windings are arranged between dielectric layers which in turn are located between ferrite cover plates. Electrical or electronic components are not included in the layer structure.
An energy supply unit for transmitting auxiliary energy is known from EP 1 310 036 B1 and comprises primary and secondary coils provided on carrier plates with an air gap therebetween. In order to extend the clearance distance between the coils, an insulating plate is disposed in the air gap which protrudes beyond the carrier plates. A layer structure of a printed circuit board is not formed in this manner.
In some electrical/electronic devices high voltages have to be handled, and for protecting against overvoltages a galvanic isolation is often provided between individual electric circuits or potential groups within the device. In order to avoid electrical flashovers in the devices, specific clearance and creepage distances for discharge currents must be kept between the electric circuits to be separated, or an insulating material of a predetermined quality and minimum thickness has to be placed between the electric circuits. Thus, there is a galvanic isolation distance between the individual electric circuits, across which electrical energy is to be exchanged, which is useful for power supply or data exchange or information exchange. This electrical energy will be referred to as an electrical signal below.
Printed circuit boards, also referred to as circuit boards or PCBs, are often used as a carrier for electrical/electronic components, assemblies and conductive traces (referred to as “components” below). Printed circuit boards may be flexible or rigid and are available in a layer structure design. For galvanic isolation between different electric circuits or potential groups on the printed circuit board it has been known to provide a “trench” on the printed circuit board, across which no component extends. The width of the isolation trench corresponds to the minimum distance in air or the minimum creepage distance along the surface of the isolation trench, which must be kept in order to achieve sufficient electrical voltage protection. The wider the isolation trench is selected on the printed circuit board, the less usable area is available for accommodating electrical/electronic components.
For signal exchange, galvanically isolated electric circuits are coupled with each other by coupling components, and for this purpose inductive and capacitive transformers or antenna systems operating in the electromagnetic near field are useful, each comprising a first and at least a second coupling element between which a solid insulating material extends. The dielectric strength of this insulating material determines the tolerable voltage difference between the potential groups or individual electric circuits.
The invention is based on the object to provide a printed circuit board with a galvanic isolation between individual electric circuits, in which comparatively high voltages between the individual electric circuits can be tolerated without having to accept comparatively large clearance and creepage distances for electrical discharge currents along the surface of the printed circuit board. Furthermore, the printed circuit board should preferably have a simple, low-cost and space-saving configuration for the accommodated components.
The invention is specified in the claims.
For galvanic isolation between the individual electric circuits, the printed circuit board comprises at least one inductive and/or capacitive transformer, each of which comprises a first and a second coupling element with an insulating barrier layer sandwiched therebetween. This insulating barrier layer provides as much as possible of the required isolation. As a result, isolation trenches for clearance and creepage distances on the printed circuit board may be largely omitted or their number may be considerably reduced. This is based on the fact that with respect to the same insulation values, the dimension of planar isolation regions for clearance and creepage distances is greater than the thickness of the insulating barrier layer. A planar isolation region refers to a surface region which extends on the printed circuit board and also around the edge of the printed circuit board and occupies a minimum distance between galvanically isolated electric circuits or potential groups, measured as a clearance and creepage distance for electrical flashover or leakage currents. A precise definition of clearance and creepage distances and their requirements can be found in the descriptions and figures of standards DIN EN 60664-1, DIN EN 60079-11/15, and DIN EN 61010-1, for example. Insulating parts mounted to the printed circuit board for enlarging the clearance and creepage distances or increasing the dimension of the planar isolation region are accordingly regarded as parts of the printed circuit board, even if these parts do not have a layer structure.
Furthermore, the reduction of space requirements on the printed circuit board by eliminating or minimizing isolation trenches results in a reduction of costs for manufacturing the printed circuit board. Structurally simple coupling elements based on planar technology allow further cost savings. In this case, the coupling elements are produced in form of loops of conductive traces or in form of capacitor plates, for example.
Specifically, with the insulating barrier layer the material of the printed circuit board itself is used as an insulating medium between adjacent electric circuits. The two opposite sides of the layer structure are utilized for the different electric circuits or potential groups, and the electrical/electronic components are mounted on both sides of the printed circuit board. Through-hole contacts across the printed circuit board through vias are largely avoided or only provided at a lateral distance from the transformers.
Exemplary embodiments of the invention will now be described with reference to the drawings, wherein:
First electric circuit 1 comprises electrical/electronic components 13 which are mounted on the free upper surface of insulating spacer layer 71 and supplied with voltage/current via conductive traces 14. Conductive traces 14 extend on both sides of insulating spacer layer 71 and are connected via contacts 8, as illustrated. Second electric circuit 2 is arranged on the upper and lower surfaces of second insulating spacer layer 72 and comprises electrical/electronic components 23 and conductive traces 24 in a similar manner as described above for electric circuit 1 with respect to components 13 and conductive traces 14. The exemplary embodiment of
For integrating printed circuit board 100 into a device, electrical connection lines 91, 92 are required for power supply and signal handling purposes. Such lines may be mounted to an insulating spacer layer 71 or 72. Furthermore, anchors in form of electrical vias 9 that extend through the layer structure of printed circuit board 100 may be provided for mounting such lines 91, 92. Such electrical vias weaken the dielectric strength of the layer structure and in particular that of insulating barrier layer 61 in a certain range which has to be considered as a minimum distance D0 to “external” or “adjacent” electric circuits. Though connection lines 91 for power and signal supply to electric circuit 1 may of course be arranged directly adjacent to elements 11, 12, 13, 14 of electric circuit 1, the minimum distance D0 which is the clearance and creepage distance to electric circuit 2 must be kept between electrical via 9 and the closest component of electric circuit 2. Similarly, the electrical via 9 which is connected to connection lines 92 must keep the minimum distance D0 to the closest components of electric circuit 1. For protecting against flashovers between the electric circuits, it is furthermore necessary to observe a minimum thickness Di of the insulating barrier layer between the electric circuits. This minimum thickness Di depends on the quality of the insulating material and the level of overvoltage that is to be tolerated. For example, if printed circuit board material FR4 is used as an insulating medium, a dielectric strength of approximately 40 kV per millimeter can be expected. Therefore, a minimum thickness of 0.2 mm would correspond to a dielectric strength of 8 kV, while a minimum thickness of 0.5 mm would accordingly exhibit a dielectric strength of 20 kV. According to various standards and guidelines, elevated security margins may result in a reduced dielectric strength or voltage class for a predetermined minimum isolation thickness.
With these measures of providing a minimum thickness Di and a minimum distance D0, the printed circuit board with layer structure configuration can be employed for high voltage applications. In this manner, voltage differences in the kV range may be handled between connection lines 91 and 92. The printed circuit board of the invention may be used in measurement devices for measuring high voltages. For example, a high voltage to be measured may be converted into a measurement signal which can be evaluated with comparatively low voltages and currents. The printed circuit board may as well be integrated in devices which are per se designed for low voltages but might be exposed to high voltages in case of failure.
For designing printed circuit boards with four or even more electric circuits that are to be separated from each other, the surfaces of the printed circuit board are divided even more intelligently and/or a plurality of insulating barrier layers are employed. As in the case of
The configuration of the described printed circuit board may be modified. For example it is possible to provide two or more insulating spacer layers one above the other, within which the components of the electric circuits are accommodated. In this case, electrical/electronic components may be mounted by surface-mount technology (SMT) and may optionally be enclosed. However, the insulating barrier layer(s) remain responsible for the high dielectric strength of the printed circuit board.
In case of three or more electric circuits to be separated, the values of Di and D0 may as well be selected to be individually different, depending on the requirements for the dielectric strength of the individual electric circuits. In case of three electric circuits to be separated, for example, three different values may be used for D0, namely D012 for separating electric circuits 1 and 2, D013 for separating electric circuits 1 and 3, and D023 for separating electric circuits 2 and 3. The same applies to Di accordingly.
Number | Date | Country | Kind |
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10 2013 100 622.1 | Jan 2013 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/050997 | 1/20/2014 | WO | 00 |