Electricity: electrical systems and devices – Safety and protection of systems and devices – Transient responsive
Reexamination Certificate
1999-05-27
2001-02-27
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Transient responsive
C361S818000
Reexamination Certificate
active
06195244
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to an electronic circuit, comprising electrical and electronic components and their connecting lines on a printed circuit board, in which case a shielded housing encloses the electronic circuit, attenuating radiofrequencies, in order to prevent interference which acts on the electronic circuit and interference which is caused by the electronic circuit, in which case the circuit has connecting lines which lead out of the shielded housing to the exterior. This circuit is intended in particular for installation in a baseplate in a motor vehicle combination instrument, in which various display instruments, display areas, monitoring and warning lights as well as the electrical and electronic equipment parts required for this purpose are arranged in a common housing and are covered by a common transparent panel.
A shielding box is known from the prior art, in which the circuit is completely surrounded by a shielding housing, and contact means in the form of contact springs connect the circuit to a baseplate which contains all the other active and passive switching elements, conductor tracks, plug connectors and connecting points which are required for operation of the combination instrument. In this case, the circuit is accommodated on a printed circuit board and is connected to the baseplate via contact springs which have different shapes and pass through the shielding housing. A disadvantage with this type of shielding is that contact means having different shapes are required. Furthermore, the known shielding housing can be assembled only with difficulty, by hand.
SUMMARY OF THE INVENTION
The object of the invention is thus to provide an electronic circuit of the type mentioned initially which provides good shielding while being of simple design and being capable of being assembled easily.
With the circuit of the invention, it is advantageous that it is possible to dispense with a retaining frame for guiding the contact means and for preventing contact between the contact means and the shielded housing. Furthermore, this type of construction means that it is possible to achieve a grid size for the individual contact means with the normal value of {fraction (1/10 )}inch (corresponding to 2.54 mm) in a row.
It is particularly advantageous for the shielding means to be designed in such a manner that contact means are provided on the printed circuit board, which are electrically conductively connected to the shielded housing, and for the contact means to be connected to the connecting lines via capacitors inside the housing. In this case it is advantageous for the filter components, in particular capacitors, to be connected as close as possible to the housing wall, in order to keep the effective length of the unprotected connecting lines as short as possible. Furthermore, it is in this case advantageous that the filter capacitors represent an economic and effective shielding means.
By using pressure contacts, it is possible in an advantageous manner to dispense with a rigid connection. At the same time, this prevents the connection from becoming loose as a result of the printed circuit board and the shielded housing having different thermal expansion levels. Furthermore, the different thermal expansion levels of the printed circuit board and of the shielded housing result in friction between the components which make contact with one another, which overcomes any contamination that may be present. The pressure contact is designed, for example, in the form of a crown.
The configuration of the contact means as solder studs is simple to construct, while at the same time being very effective. Furthermore, it is advantageous in this context that the solder studs can be produced at the same time as the connections for the SMDs.
An electrically highly conductive connection between the individual contact means and a ground ring line prevents possible potential differences and enhances the radio-frequency shielding of the shielded housing overall.
The plated through holes for the ring lines at the same time act as a shielding grid. Where shielding must be provided for frequencies up to 1 GHz, it has been found to be advantageous for the distance between the individual contact point s to be about 12 mm.
Pushing the side parts of the shielded housing against the contact means results in an economic and effective pressure-contact connection between the shielded housing and the filter components.
The use of galvanized ferromagnetic sheeting for the shielded housing and solder studs composed of tin prevent contact oxidation of the conductor tracks, and thus ensures good electrical connection.
The fact that the printed circuit board has slots through which the lugs on the shielded housing are passed means that an electrical connection and mechanical joint can be produced in a simple way between the shielded housing case and the shielded housing cover by bending the lugs around, for example, the shielded housing cover. Furthermore, the bending of the lugs at the same time fixes the shielded housing on the printed circuit board in such a manner that the housing is permanently pressed against the contact means. The lugs also act as plated-through holes to the cover.
The use of aluminum-oxide ceramic for the printed circuit board ensures good heat dissipation for the components.
The multilayer technology allows complex circuits in a very small space.
Finally, if the capacitors are tuned to the interference frequency having the greatest amplitude on the respective lines, the interference is suppressed as well as possible.
If contact springs are used as the connecting means, it is possible to compensate for the different thermal expansion levels between the printed circuit board and the baseplate, without any mechanical stresses.
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Farber Martin A.
Mannesmann VDO AG
Sherry Michael J.
LandOfFree
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