Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
1998-07-20
2001-11-27
Cuchlinski, Jr., William A. (Department: 3661)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C361S752000, C361S753000, C361S799000, C361S800000, C361S816000, C361S818000, C174S034000, C174S034000, C174S050510, C029S729000
Reexamination Certificate
active
06323418
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electrically screening housing for accommodating and electromagnetically screening assemblies which emit electromagnetic radiation, according to the preamble of claim
1
.
It is known to make electrically screening housings from electrically non-conductive material, particularly plastic, by coating the prefabricated housing parts with a conductive material, e.g. by spraying them with conductive lacquer or applying aluminium by vapour deposition (cf. “Kunststoffgehause und EMV”, elektronikindustrie 3—1992, p. 42). Such housings were generally provided with prefabricated seals made of conductive elastomer which were put in place during assembly. DE 38 12 943 A1 discloses an internally coated screening housing of fibre-reinforced plastic with a prefabricated seal of this kind placed between the groove and tongue.
Housings of the type described above—which have achieved particularly marked economic significance with the rapid proliferation of mobile telephones—are also known from EP 0 629 114 B1 and EP 0 654 962 A1.
The housings described therein are made up of two parts which consist of electrically conductive material or are coated with such for the purpose of electrically screening the inside of the housing (at least in parts) and in the assembled state form a Faraday cage. For electromagnetically screening the housing in the area of the joint between the adjoining housing parts there is also a screening seal which consists of an electrically conductive and at the same time elastic material and adapts to surface tolerances and unevenness, so that a very high quality screening of the inside of the housing can be ensured even with large-scale mass production. According to the specifications referred to above, this screening seal is produced directly on at least one of the housing parts, whilst an additional carrier may also be included in the construction.
By virtue of this construction the housing is easy to open, e.g. for maintenance purposes or for changing a battery in the housing, and is easily resealed afterwards whilst retaining the screening effect.
However, when producing a material for the screening seal, it is difficult for certain applications to achieve the best possible compromise between high elasticity, high conductivity and lowest possible material costs. A material which is advantageous from the physical point of view is a plastics composition filled with a high proportion of silver powder, but this is relatively expensive.
SUMMARY OF THE INVENTION
The aim of the invention is therefore to provide an electrically screening housing of the type mentioned hereinbefore which is cheap to manufacture.
In order to reduce costs, the present invention teaches that the screening seal is not made entirely from an electrically conductive flexible material, but rather that the joints be filled on site using a substantially electrically non-conductive ductile (elastic) element. The electrical screening in the joint area join by a further layer of electrically conductive material adhering to the substantially electrically non-conductive ductile element which is merged into the screening of the substantially rigid walls of the housing.
The sealing element primarily has the function of filling the interstice of the joint so as, for example, to reliably protect the inside of the housing from moisture and dust, in the event of any mechanical play between the housing parts caused by manufacturing errors or surface unevenness, and to prevent relative movements between the housing parts. As a result of the improved mechanical properties of the sealing mass it is thus possible to provide a durable hermetic seal for the inside of the housing. At the same time the sealing element provides part of the electromagnetic screening and ensures that it is sealed. It is particularly advantageous in this respect to use a high-grade elastic material and/or a flexibly shaped seal by means of which a prestress is built up between the housing parts during the assembly of the housing parts by the compression and/or bending of the sealing element, capable of preventing the undoing of a screw or clamp connection. However, the invention is not restricted to the use of carrier elements which are elastic by their material and/or shape, but can in principle also be performed with a plastically deformable sealing element.
In the preferred embodiment of the invention, the covering consisting of electrically conductive material is applied cohesively (and particularly in a single operation) to the surface of the sealing element and the rigid housing wall.
In another alternative embodiment of the invention the screening is of a sandwich construction, and the carrier element consists of at least two layers of electrically. non-conductive but flexible material between which is provided the layer of electrically conductive material which brings about the electromagnetic screening. The arrangement of the layer of electrically conductive material in a substantially deformation-free area between two deformable layers or strips of the elastic element advantageously counteracts cracking in the electrically conductive material, which is particularly important for constructions in which severe deformation of the screening element is supposed to occur or may occur when the housing parts are put together.
In another advantageous embodiment, it is proposed that the layer of electrically conductive material be made very thin in order to prevent cracking, since the bending stresses and hence the tendency to cracking increase as the layer thickness increases for a given amount of bending. The thickness of the layer of electrically conductive material is therefore substantially less (preferably by one to three orders of magnitude) than the width of the joint.
The application of the screening layer to the sealing element or—in the case of a sandwich construction—to one layer or strip thereof may be effected by various methods. Suitable methods of achieving uniform layer thicknesses are the processes known per se of spraying with conductive lacquer or spraying with a pure metal, but particularly galvanic metallisation and the processes of gas phase deposition (known especially from the manufacture of electronic components) such as sputtering and CVD (chemical vapour deposition).
In an advantageous embodiment, within the scope of the processes mentioned above, the coating is produced by the controlled growth of crystallites in accordance with the structurally predetermined directions of mechanical stressing of the substrate (especially the sealing element). Small lamellar surface elements may be formed on the surface—particularly in a multilayered structure—which cohere only loosely within the layer and are thus movable relative to one another to some extent during bending of the carrier element, which also counteract any cracking in the screening layer. It is particularly favourable if said crystallites are arranged in the manner of scales or roof-tiles, which can be achieved by angled spraying or sputtering of a suitable substrate with an appropriate choice of the coating parameters, i.e. apart from the orientation of the substrate, the substrate temperature, the flow rate of the gas, etc.
In another alternative embodiment of the invention the application of the electrically conductive layer to the carrier element is not carried out in the mechanically tension-free state but in a state of predetermined compression and/or bending of the sealing element. This ensures that cracking in the electrically conductive layer does not lead to a reduction in the electromagnetic screening action of the screening element. In this embodiment, the invention starts from the idea that cracking in the electrically conductive layer is difficult to prevent under all circumstances owing to the deformation of the screening element which occurs during the assembly of the housing, which means that it is important to minimise the negative effects of such cracking on the electromagnetic screening cha
Kahl Helmut
Tiburtius Bernd
Cuchlinski Jr. William A.
Mancho Ronnie
Spencer George H.
Venable
Wood Allen
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