Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-12-02
2001-12-04
Gandhi, Jayprakash N. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S736000, C361S742000, C361S752000, C361S753000, C361S801000, C361S816000, C174S13800J
Reexamination Certificate
active
06327156
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a modular housing for a substrate with electronic components, wherein the housing comprises at least a base part and a cover part, wherein the parts of the housing consist of an electrically conductive material for electromagnetic shielding and form outer walls enclosing a space inside the housing which accommodates the substrate, wherein dividing walls extend in the space inside the housing and have free edges which support the substrate.
Electronic components which are mounted on a substrate, generally a printed circuit board, are often enclosed in a housing which consists of an electrically conductive material for electromagnetic shielding. To allow easy assembling and dismantling of the housing, e.g. for service purposes, it consists generally of two or more parts which are fixed to each other by connection means, for example screws.
In some cases, it is necessary to shield different sections of a substrate against each other because interference may disturb the circuits, especially if radio frequency circuits are mounted on the substrate. For this purpose, a housing with dividing walls inside the space for the substrate is described in U.S. Pat. No. 4,661,888. The housing consists of a base plate and two cover plates on opposite sides of the base. Both the base and the covers have dividing walls supporting a substrate which is located between the base and a cover. The free edges of the dividing walls contact continuous grounding strip conductors on the substrate. In this way, different sections of the substrate are shielded against each other. The contact between the walls and the conducting strips is improved by conductive elastomer gaskets which are disposed on the edges of the walls.
In the design described above, the connecting means press the parts of the housing onto the opposing sides of the substrate, i. e. the substrate separates the parts from each other. Consequently, the mechanical stability of the housing is limited by the properties of the substrate. In most cases, the thermal expansion coefficients of the housing and the substrate differ. This causes mechanical stress which may lead to damage of the electronic circuits on the substrate when the housing is subject to temperature changes resulting from external influences or heat generation from components inside. Mechanical stress can also be caused by tolerances in the dimensions of the parts or improper fixing of the parts to each other. Finally, in the state of the art the cooling of the components in the housing is achieved by air circulation through holes in the outer walls which impair the shielding. However, thermal air circulation is not possible for space applications. Consequently, other means for heat dissipation have to be developed.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to obviate these disadvantages and develop a modular shielding housing which is strong and avoids mechanical stress of the substrate. It is a further object to provide a housing which has a good heat dissipation from the electronic components enclosed inside without using air circulation. Still another object of the present invention is to develop a housing which is optimized for minimum mass.
According to the present invention, at least one of said parts is provided with spacers which are in mechanical and thermal contact with an adjacent part and which define the height of the space inside the housing.
The basic concept of the invention is to provide spacers which extend through the space inside the housing. The spacers form a continuous mechanical and thermal connection between adjacent parts of the housing. Consequently, they define the height of the space inside. The free space is dimensioned to accommodate the substrate with the electronic components. For this purpose, the spacers ensure that there is a gap between the dividing walls on opposing sides of a substrate and the width of the gap is at least equal to the thickness of the substrate. A preferred shape of the parts are slices aligned parallel to the substrates.
Generally, there is some free space around the substrate, especially at its edges, to allow for thermal expansion. The clearances at the edges of a substrate are limited by the outer walls of the housing and the spacers. It is possible that there is only one substrate between two adjacent parts of the housing but there may also be several substrates in the same plane if the space is sufficient.
The connections from the substrates to elements outside of the housing or between different substrates are obtained preferably by flexible or semi-flexible connections. Alternatively, sliding connections may be used. In many cases it is of advantage if connections from the housing to outside components are located only on one of its parts, preferably on the base part. This allows to open the housing, e.g. for service or adjustment, by removal of the cover while leaving the connections in place. To ensure a sufficient cooling of the housing, one of its parts, preferably the base, can be coupled to a supporting structure which dissipates the heat.
The proposed design has the advantage that mechanical forces on the housing, especially pressures, are not transferred to the substrate inside but rather by the spacers between the outer walls. Furthermore, the spacers conduct heat generated inside the housing by thermal contact to its outer walls. Because the spacers in conjunction with the dividing walls improve the stability of the housing, the weight may be low while retaining a good stability.
In an advantageous embodiment of the invention, the housing comprises one or more intermediate parts located between the base part and the cover part. In this case, a substrate can be located in a gap between the base part and an intermediate part, between the cover part and an intermediate part or between two intermediate parts. The modular construction offers the opportunity to adapt the size of the housing to different numbers of substrates by using different numbers of intermediate parts. Like the base and the cover part, the intermediate parts are provided with dividing walls for supporting one or several substrates. The intermediate parts are also provided with spacers for defining the height of the space inside the housing, especially the width of the gaps for accommodating the substrates.
Preferably, the parts of the housing are one-piece parts comprising the outer walls, the dividing walls and the spacers. The parts may either be machined parts or castings, facilitating a suitable shape and size of the housing. A good electrical conductivity and a low mass of the housing can be attained by parts made from aluminum or a magnesium alloy.
The spacers may be located exclusively on one of the adjacent parts and extend all the way through the space inside the housing to the outer wall of another part. It is preferred, however, that a spacer touches the face of another spacer in the adjacent part of the housing. In this case, the spacers are segments of a larger mechanical and thermal connection through the housing.
Fastening means are of advantage to join different parts of the housing to each other and the housing to a support. Suitable means are for example screws or pin screws. In a preferred embodiment of the invention, some or all spacers include a hole to accommodate the fastening means. The location of the fastening means inside the spacers reduces strains in the housing. In addition, a good thermal and mechanical contact between the spacer and an adjacent part of the housing, especially between adjacent spacers is ensured. Especially if the fastening means are used to attach the housing to a support, continuous holes running through the whole housing are preferred. It is, however, possible that holes extend only through a part of a spacer. If screws are used as a fastening means, the inner surfaces of the holes may be threaded.
The spacers can be located at any position inside the housing which is suitable to attain a good mechanica
Alcatel
Gandhi Jayprakash N.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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