Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Patent
1995-08-02
1996-05-28
Ledynh, Bot L.
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
361302, 361330, 333182, 439620, H01G 438, H03H 700
Patent
active
055217842
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a filter unit for connectors comprising:
at least one substrate made of electrically insulating material and having two mutually opposite sides and through openings for contact elements of the connector;
capacitors situated on at least one of the two opposite sides of the substrate in the region of the through openings, each of said capacitors comprising at least one first conducting layer in contact with the substrate, a dielectric layer and a second conducting layer; and
at least one passivating, electrically insulating cover layer disposed above each of said capacitors, said cover layer comprising at least one first flexible passivating, electrically insulating layer having a low moisture absorption coefficient, and a second hard layer.
Such a filter unit is disclosed by European Patent Application EP-A-0 124 264.
In electrical transmission engineering, pulse-type signals are increasingly being used to transmit information. As known in electrical engineering, pulse-type signals can be broken down into a series of sinusoidal signals having increasing frequency, the so-called higher harmonics. In the case of signals having a high pulse frequency, as is usual in the case of computers, higher harmonics may occur in the megahertz region or even up into the gigahertz region.
The steepness of the pulse edges, also referred to as the rise time, likewise plays an important role. A normal rise time of one nanosecond corresponds to a higher harmonic frequency of approximately 350 MHz, regardless of the pulse frequency itself.
Such higher harmonics are found to be very troublesome. In a space in which various interconnected electronic processing apparatuses which generate pulse-type signals are present, interferences readily occur in the information processing as a consequence of the higher harmonic signals. Such interferences may assume a proportion such that the correct functioning of, for example, computers is no longer possible.
In order to be able to keep the total interference level as low as possible, it is necessary to use filters with which the undesirable higher harmonic frequencies can be attenuated without the desired information signal being excessively distorted. A capacitor is a component which is suitable for this purpose because its reactance is inversely proportional to the frequency. That is to say, the reactance is greater for relatively low frequencies than for higher frequencies.
European Patent Application 0,124,264, referred to above, discloses a filter unit for connectors in which two cover layers may be used on the capacitors. An inner cover layer covering the capacitor is composed of glass and an outer cover layer covering the inner cover layer is made of silicone. This known combination of cover layers is unsuitable for fairly large surface areas because, in that case, the mechanical stresses in the glass become too high with increasing temperature owing to the different temperature coefficients and cracks may occur. Because the outer layer is composed of silicone, which has a high moisture diffusion coefficient, moisture is then able to penetrate the capacitors via the two cover layers.
In another filter unit, as described in EP-A-0,299,563, each of the contact devices of a connector is decoupled to earth (chassis) with the aid of a capacitor. The filter unit is manufactured by the so-called thick-film screen-printing technology on a flat substrate. Such methods permit capacitors to be inexpensively manufactured which have an inductance low enough to attenuate signals effectively at high frequencies. The capacitance value of the flat capacitors produced in this way is directly proportional to the surface area of the mutually opposite electrodes and the relative permittivity of the dielectric material present in between, but is inversely proportional to the distance between the electrodes.
In the filter unit, known from EP-A-0,299,563 the capacitors are covered with a protective cover layer, which may be made up of various sublayers.
REFERENCES:
patent: 4611882 (1986-09-01), Ushida
patent: 4682129 (1987-07-01), Bakermans et al.
patent: 4791391 (1988-12-01), Linnell et al.
patent: 4931754 (1990-06-01), Moussie
patent: 5130780 (1992-07-01), Kumai et al.
patent: 5150086 (1992-09-01), Ito
patent: 5167539 (1992-12-01), Okamoto et al.
Berg Technology Inc.
Ledynh Bot L.
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