The invention relates to a printed circuit board, an electrical appliance with said printed circuit board, and a method of manufacturing the printed circuit board.

Printed circuit boards with SMD components are used in modem electrical appliances. SMD components ("Surface Mounted Devices") are components mounted on a surface of the printed circuit board. During mounting of the printed circuit board, first a soldering paste is provided on the printed circuit board in a given pattern by means of a silk- screen printing method. Then the SMD components are laid on the printed circuit board and are fixed to the surface thereof, possibly by means of a non-conductive adhesive, such that the connection terminals of the components come into contact with the soldering paste pattern printed on the printed circuit board in given locations. The components themselves and their connection terminals will then be on one and the same side of the printed circuit board. Then a so-called reflow soldering process is carried out. During this, the solder provided on the printed circuit board is melted through heat supply in a suitable oven such that fixed soldered electrical connections are created between the SMD components and the printed circuit board.

Electrical appliances often require coils which are mounted on the printed circuit boards mentioned above of the respective electrical appliances. The mounting of the coils is problematic in that the coils must be provided manually to the printed circuit board.

For this purpose, the two winding ends of each coil are inserted into respective bores of the printed circuit board, during which they press away the soldering paste provided on the bores and at the lower side of the printed circuit board. No fixed soldered electrical connections can be made between the coils and the printed circuit board in the ensuing soldering process.

The document DE 100 16 974 Al describes a coil with a plurality of turns which comprise a magnetic material. The coil is mounted on a printed circuit board in that winding ends of the coil are inserted into two bores of a printed circuit board. The document further discloses a coil which is fastened on an upper side of the printed circuit board without bores by the SMD technology. Its winding ends are for this purpose horizontally aligned and are subsequently mounted to the surface of the printed circuit board.

Since the coils are aligned after being fastened to the printed circuit board so as to achieve a desired inductance of the coils, distances between the turns are mechanically changed in that they are widened. This strongly loads the previously created soldered joints of the coil mechanically, so that the alignment of the coil often results in a destruction of the soldered joint.

The invention has for its object to provide a printed circuit board which has coils whose mounting is as cost-effective as possible.

The object is achieved in that the printed circuit board comprises a coil which is surface-mounted on a first side of the printed circuit board and whose winding projects from the second side of the printed circuit board opposed to the first side and lies at least partly in a void of the printed circuit board.

The mounting of the coil which is present in a void of the printed circuit board may be integrated into a single soldering process of the entire printed circuit board.

Additional soldering processes which only served to contact the coil on the printed circuit board become redundant. The mounting cost for the coils can thus be reduced. The positioning of the winding of the coil in the void of the printed circuit board stabilizes the coil in its position thanks to the inner edges of the void in the printed circuit board, so that tilting during alignment of the coil is not possible, and a mechanical load exerted on the soldered joints can be reduced.

Given a size of the void which corresponds to the diameter of the winding, i. e. the void is large enough for accommodating the winding fully, the coil will be particularly well supported by the printed circuit board, and the winding ends of the coil can be electrically contacted with a conductor track on a surface of the printed circuit board by means of a soldering process without problems.

The invention also relates to an electrical appliance comprising a printed circuit board according to the invention. For example, the printed circuit board may be used in electrical appliances in the field of consumer electronics which are mass-manufactured.

The invention further relates to a method of manufacturing a printed circuit board, in which method components are electrically contacted with the printed circuit board by means of a soldering process. For this purpose, a coil is arranged after the provision of the soldering paste used for the soldering process such that it can be surface-mounted to a first side of the printed circuit board, while its winding projects from a second side of the printed circuit board. The coil is contacted with the printed circuit board by means of the soldering process, for which preferably a reflow soldering process is chosen.

An embodiment of the present invention will be explained in more detail below with reference to several Figures, of which: Fig. 1 shows a coil fastened to a printed circuit board in a conventional manner, Fig. 2 shows the coil mounted in SMD technology, Fig. 3 shows a printed circuit board according to the invention with coil in side elevation, Fig. 4 shows a void in the printed circuit board fitting the coil, Fig. 5 shows the printed circuit board and coil according to the invention in plan view, Fig. 6 shows the printed circuit board and coil according to the invention in a further side elevation, and Figs. 7 to 9 show the printed circuit board and coil according to the invention after an alignment of the coil.

Fig. 1 shows a coil 1 with winding ends 2 and 3 fastened to a printed circuit board 4 in a conventional manner. Conventionally mounted coils 1 with a plurality of turns involve the problem that winding ends 2 and 3 of the coil 1 are to be inserted into two comparatively small holes of the printed circuit board 4. While being inserted, the winding ends 2 and 3 press the soldering paste provided on the lower side of the printed circuit board aside, so that no electrical connections can be created in the soldering process.

The coil 1 shown in Fig. 2 is mounted in a known manner to the printed circuit board 4 in SMD technology. The coil 1 and its winding ends 2 and 3 are present on the upper side of the printed circuit board 4. The winding ends 2 and 3 are fastened in planar manner, which renders holes through the printed circuit board 4 redundant and do away with an additional soldering process on the lower side of the printed circuit board.

To achieve a certain inductance of the coil 1, the latter is mechanically corrected in that the distances between the turns are widened. It is in particular coils with a small number of turns that become unstable owing to the mechanical load on the soldered joint and tend to tilt over. The electrical connection with a conductor track on the printed circuit board 4 is destroyed thereby.

Fig. 3 is a side elevation of the printed circuit board 4 according to the invention with a coil 1. The printed circuit board 4 has a void 5 of sufficient size for the coil 1 to be inserted with its turns into the void. The winding ends 2 and 3 of the coil 1 are fastened to the lower side of the conductor track 4 and are electrically connected to a

conductor track. During the alignment of the turns, the coil 1 is stabilized by the printed circuit board 4, and the soldered joints of the winding ends 2 and 3 are mechanically loaded to a much lesser degree.

Figs. 4 and 5 each show a plan view of the printed circuit board 4. In Fig. 4, there is no coil 1 in the void 5 of the printed circuit board 4, whereas Fig. 5 shows the printed circuit board 4 with coil 1. A side elevation of the printed circuit board 4 according to the invention with the coil 1 is shown in Fig. 6. The side elevation makes it clear that the turns project for a major portion beyond the upper side of the printed circuit board, while the winding ends 2 and 3 are fastened to the lower side of the printed circuit board 4 in a planar arrangement.

Figs. 7 to 9 are further side elevations showing the alignment of the coil 1 achieved by means of changes in the turns without an instability of the coil 1 arising therefrom.