SEALED PACKAGING FOR ENVIRONMENTAL PROTECTION OF ELECTRONICS

Abstract: A telecommunications active electrical circuit apparatus, comprising: (a) a circuit board having active components; (b) a flexible environmental gas and liquid barrier envelope sealingly encapsulating at least part of said circuit board; and (c) an electrical connector for connecting the circuit board to an external system, whereby said connector is located outside the flexible barrier envelope and is electrically connected to the circuit board by means of one or more flexible electrical conductors extending out of the flexible envelope.

Description: Sealed Packaging For Environmental Protection Of Electronics This invention relates to environmental protection for active electronics. More specifically, this invention relates to sealed packaging for the environmental protection of active electronic circuit boards, e.g. for telecommunications. Traditionally, most of the electronics in a telephony network has been located in the central office or in a few large electronic installations located remotely from the central office. These remote electronics are powered by power drawn from the power mains and backed up by battery power supplies. The electronics in the central office operate in an environment with a carefully regulated temperature and humidity to assure their proper operation. The remote electronics are usually also installed in vaults with controlled environments, or at least in enclosures that are maintained at a temperature above that of the outdoor environment by the large amount heat dissipated by the system. Recent advances in digital signal processing have made possible new and more capable transmission systems. Many of these new systems have created a need to move the active electronic components in the telephone system away from a temperature controlled central office and out into the general environment where the components will be exposed to wide fluctuations in temperature and environmental pollutants. To gain the full advantage of these new transmission systems it is desirable to deploy the remote electronics in small units that are powered from a central point over the transmission media. These power efficient units generate very little heat and so are much more vulnerable to damage from moisture than was the case in the past because they lack the internal heating necessary to keep them dry. As a result there has been an increasing need for environmental protection of these low heat-generating active electronics systems. The typical small remote electronics units deployed in the telecommunications network will be installed by technicians with few tools and limited supervision. The service life of these electronics is expected to be many (e.g. 20) years. According to a first aspect of the present invention, there is provided a telecommunications active electrical circuit apparatus comprising: (a) a circuit board having active components; (b) a flexible environmental gas and liquid barrier envelope sealingly encapsulating at least part of said circuit board; and (c) an electrical connector for connecting the circuit board to an external system, whereby said connector is located outside the flexible barrier envelope and is electrically connected to the circuit board by means of one or more flexible electrical conductors extending out of the flexible envelope. The first aspect of the invention has the advantage that because the circuit board is sealingly encapsulated in a flexible environmental gas and liquid barrier envelope, it is normally well protected from such environmental hazards even when the apparatus is located remotely from the central office and the electrical or electronic components of the circuit board do not generate very much heat. This advantage is combined with the advantage that the electrical connection between the circuit board and an external system is via an external electrical connector which is itself electrically connected to the circuit board via one or more flexible electrical conductors extending out of the sealed flexible envelope. This means that the circuit board may remain sealed from the environment even when, in use, electrical connections with the circuit board are made, broken or changed. In a preferred embodiment of the first aspect of the invention, the apparatus further comprises a casing which, at least in use, contains the electrical connector and preferably also sealingly encapsulates part only of the flexible envelope, and the exit of the or each electrical conductor out of the envelope. According to a second aspect of the invention, there is provided a telecommunications active electrical circuit apparatus, comprising: (a) a circuit board having active components; (b) a flexible environmental gas and liquid barrier envelope encapsulating at least part of said circuit board; (c) an electrical connector for connecting the circuit board to an external system, whereby said connector is located outside the flexible barrier envelope and, at least in use, is electrically connected to the circuit board by means of one or more electrical conductors extending out of the flexible envelope; and (d) a casing which, at least in use, contains the electrical connector and also sealingly encapsulates part only of the flexible envelope and the exit of the or each electrical conductor out of the envelope. The second aspect of the invention, and the preferred embodiment of the first aspect of the invention, have the advantage that, because the casing which contains the electrical connector also sealingly encapsulates part of the flexible envelope, and the exit of the or each electrical conductor out of the envelope, the exit of the electrical conductor(s) from the flexible envelope is sealed in a simple yet highly effective manner. This is advantageous because the exit for the electrical conductor(s) is normally the most difficult part of the flexible envelope to seal effectively. It has been found that when adhesives, mastics, and even high-performance sealing materials such as gels (as described below) are used to provide a seal between the electrical conductors and the flexible envelope, it often cannot be guaranteed that such a seal will not fail. The second aspect of the invention, and the preferred embodiment of the first aspect of the invention, overcome this problem by using a casing, which also contains (preferably sealingly) the electrical connector, to provide the required seal. The casing may, and preferably does, provide this seal by being sealed, itself, by means of sealing material (e.g. gel). The electrical conductor(s) of either aspect of the invention may comprise one or more wires and /or at least one flat cable. The electrical conductor(s) of the second aspect of the invention may, alternatively, be carried by a relatively narrow extension of the circuit board, which extends from a relatively wide main portion of the circuit board which carries the active components. The flexible envelope may advantageously comprise a relatively wide portion which encapsulates the circuit board, or at least a main portion thereof, and extending from the wide portion a relatively narrow portion which encapsulates at least part of the or each electrical conductor. Preferably, the relatively narrow portion of the envelope extends into the casing which contains the electrical connector. The flexible envelope is preferably substantially impervious to water, and more preferably is substantially impervious to water in both liquid and vapour phases. The envelope is preferably formed from polymeric material (e.g. polyester and/or polyethylene). Advantageously, the envelope wall(s) comprise(s) one or more layer(s) of polymeric material and one or more layer(s) of metal (e.g. aluminium). A particularly preferred envelope wall comprises a metal layer sandwiched between two polymeric layers. The presence of a metal layer normally makes the envelope wall(s) substantially impervious to water vapour. Any joins in the wall(s) of the envelope are preferably formed (and sealed) by heat-welding polymeric layers of the wall(s) together. The flexible envelope preferably has the form of a sealed bag or the like. It may be formed for example, from one or more sheets, the edges of which are preferably bonded or welded together. For the avoidance of doubt, it should be noted that the electrical connector may comprise a single electrical connector or a plurality of electrical connectors, either joined together, or separate from each other. The casing for the electrical connector preferably comprises at least two parts which are brought together, in use, to contain the electrical connector. The parts of the casing may be secured together in any of a variety of ways, e.g. they may be snap-fitted together, or screwed or bolted together, etc. The two (or more) parts of the casing may be separate parts or they may be joined, e.g. hinged, together. The casing preferably contains sealing material which sealingly encapsulates part of the flexible envelope and the exit of the or each electrical conductor out of the envelope. The sealing material preferably also seals the electrical connector from the environment. Generally any sealing material may be used, e.g. elastomeric material (especially natural or synthetic rubber), polymeric foam material, mastic, grease (e.g. silicone grease) or gel. The preferred sealing material comprises gel. The gel may, for example, comprise silicone gel, urea gel, urethane gel, thermoplastic gel, or any suitable gel or gelloid sealing material. Preferred gels comprise liquid (e.g. oil)-extended polymer compositions. The polymer composition of the gel may for example comprise an elastomer, or a block copolymer having relatively hard blocks and relatively elastomeric blocks. Examples of such copolymers include styrene-diene block copolymers, for example styrene-butadiene or styrene-isoprene diblock or triblock copolymers, e.g. as disclosed in International Patent Application WO 88/00603. Preferably, however, the polymer composition comprises one or more styrene-ethylene-propylene-styrene block copolymers. The extender liquids employed in the gel preferably comprise oils. The oils may be hydrocarbon oils, for example paraffinic or napthenic oils, synthetic oils for example polybutene or polypropene oils, or mixtures thereof. The preferred oils are mixtures of non-aromatic paraffins and naphthenic hydrocarbon oils. The gel may contain additives, e.g. such as moisture scavengers (e.g. Benzoyl Chloride), antioxidants, pigments and fungicides. Examples of gels are disclosed in US Patent 4634207 (Raychem), the disclosure of which is incorporated herein by reference. The invention will now be described, by way of example, with reference to the accompanying drawings, of which: Figure 1 is an illustration of a circuit board with connection wires attached to it, prior to being encapsulated by a flexible environmental gas and liquid barrier envelope; Figure 2 is an illustration of an apparatus according to the invention; Figure 3 is an illustration of a circuit board with an electrical connector mounted on an extension of the board, prior to being encapsulated by a flexible environmental gas and liquid barrier envelope; Figure 4 is an illustration of a main portion of the circuit board of Figure 3 encapsulated by the flexible envelope, and with the extension carrying the connector extending out of the envelope, prior to two parts of a casing for the connector being brought together around the connector and the exit of the circuit board extension from the envelope; Figure 5 is an illustration of the apparatus shown in Figure 4, after the two casing parts have been brought together; Figure 6 is an illustration of one type of flexible envelope used in the invention, encapsulating a circuit board; Figure 7 is an illustration of an apparatus according to the invention contained in an outer box; Figure 8 is an illustration of another type of flexible envelope used in the invention, encapsulating a circuit board; and Figure 9 is an illustration of another apparatus according to the invention contained in an outer box. Figure 1 shows a printed circuit board 1 carrying electrical/electronic components 8, and a plurality of insulated connection wires 2 extending from the circuit board. A flexible envelope comprising two laminate sheets 3, 4 are shown disposed above and below the circuit board 1. The laminates 3, 4 may be of or similar to the material used in the product known by the Trademark, "TDUX" commercially available from Raychem. Such laminates comprise sheets of aluminium or other metal foil and polymeric strength and tie layers, such as polyester and copolymer (e.g. ethylene vinyl acetate) layers respectively. Figure 2 shows the result of encapsulating the circuit board 1 between the sheets 3 and 4. The sheets are joined together by welding or bonding to seal the edges. The connecting wires are sealed at the edge at which they pass out from between the sheets. The sheets 3, 4 are provided with openings 5 by which the encapsulated board may be fixed in place in a supporting structure, e.g. an outer box (not shown). The connection wires 2 are connected to an electrical connector 6. This connector may comprise individual connectors having an aperture in each side in which a wire or other conductor can be inserted. The individual connectors are contained in a two part casing 7, 9 which is substantially filled with gel or other sealing material. When the two parts are brought together the gel is displaced so as to provide environmental protection for the connectors. One or more perforated lugs 11 may be provided for attaching the connector 6 to a suitable support (not shown). Figure 3 shows a printed circuit board 1 with sheets of laminate 3, 4 disposed above and below it. The board 1 has an extension 13 carrying a connector 6 linked to components on the board by conductive tracks (not shown). The sheets of laminate are of such a size that when brought together and sealed at the edges they will encapsulate the main portion of circuit board 1 but not the extension 13 or connector 6. Figure 4 shows a main portion 15 of the circuit board of Figure 3 encapsulated by the flexible envelope, and with the extension 13 carrying the connector 6 extending out of the envelope 1, 3, prior to two parts 17, 19, of a casing for the connector being brought together around the connector and the exit 18 of the circuit board extension 13 from the envelope 1, 3, as shown in Figure 5. Each casing part 17, 19, has a coating of sealing material 21, which seals between the parts 17 and 19, and the exit 18 of the circuit board extension 13 from the envelope. Figure 6 shows one form of flexible envelope containing a circuit board 1. The envelope comprises two sheets 3, 4, of a laminate comprising an inner aluminium layer sandwiched between two outer polyester layers, the sheets having been heat- welded together at their edges 23 in order to form the envelope. Prior to welding the sheets together, a circuit board 1, containing the electrical electronic devices (e.g. for multiplexing telecommunications signals), was inserted between the sheets. A flat cable 25 electrically connected to the circuit board 1 extends out of the sealed flexible envelope, and sealing material 21, preferably mastic or gel, seals between the envelope and the flat cable at the exit region 18, to ensure that the interior of the envelope is completely sealed from the outside environment. Advantageously, the envelope may contain desiccant to ensure that any moisture trapped inside it, or any moisture ingressing into it, does not damage the electronics. Figure 7 is a schematic illustration of a fully assembled apparatus according to the invention, illustrating the general arrangement of the flexible envelope 3, 4 contained in an outer box 27. Electrical conductors, preferably in the form of a flat cable 25, extend out of the envelope and are electrically connected to an electrical connector 6 which is contained in a casing 7, 9 (which is attached to the outer box in a cut-away region of the outer box). Additional electrical conductors 29 (e.g. wires) are electrically connected to the electrical connector 6 and extend out of the apparatus, to connect the electronics encapsulated in the envelope to an outside system. Figure 8 shows another type of flexible envelope used in the invention, encapsulating a circuit board 1 and a flat cable 25 electrically connected to the flat cable. The flexible envelope comprises a relatively wide portion 31 which encapsulates the circuit board, and extending from the wide portion a relatively narrow portion 33 which encapsulates the flat cable 25. The wide portion and the narrow portion may be portions of a single integral envelope, or they may be separate portions which are joined, e.g. welded, together. Figure 9 shows the circuit board 1 and flat cable 25 encapsulated in the flexible envelope 3, 4 of Figure 8 contained in an outer box 27. An electrical connector 6, which is contained in a casing 7, 9 is electrically connected to the flat cable 25. The narrow portion 33 of the flexible envelope extends into the casing 7, 9.

Claims: CLAIMS 1. A telecommunications active electrical circuit apparatus, comprising: (a) a circuit board having active components; (b) a flexible environmental gas and liquid barrier envelope sealingly encapsulating at least part of said circuit board; and (c) an electrical connector for connecting the circuit board to an external system, whereby said connector is located outside the flexible barrier envelope and is electrically connected to the circuit board by means of one or more flexible electrical conductors extending out of the flexible envelope. 2. An apparatus according to claim 1, which further comprises: (d) a casing which, at least in use, contains the electrical connector and also sealingly encapsulates part only of the flexible envelope, and the exit of the or each electrical conductor out of the envelope. 3. A telecommunications active electrical circuit apparatus, comprising: (a) a circuit board having active components; (b) a flexible environmental gas and liquid barrier envelope sealingly encapsulating at least part of said circuit board; (c) an electrical connector for connecting the circuit board to an external system, whereby said connector is located outside the flexible barrier envelope and, at least in use, is electrically connected to the circuit board by means of one or more electrical conductors extending out of the flexible envelope; and (d) a casing which, at least in use, contains the electrical connector and also sealingly encapsulates part only of the flexible envelope, and the exit of the or each electrical conductor out of the envelope. 4. An apparatus according to claim 2 or claim 3, in which the flexible envelope comprises a relatively wide portion which encapsulates the circuit board, or at least a main portion thereof which carries the active components, and extending from the JO- wide portion a relatively narrow portion which encapsulates at least part of the or each electrical conductor. 5. An apparatus according to any preceding claim, in which said electrical conductor(s) comprise(s) one or more wires and/or at least one flat cable. 6. An apparatus according to claim 3 or claim 4, in which the or each said electrical conductor is carried by a relatively narrow extension of the circuit board, which extends from a relatively wide main portion of the circuit board which carries the active components. 7. An apparatus according to any one of claims 2 to 6, in which the casing comprises at least two parts which are brought together, in use, to contain the electrical connector. 8. An apparatus according to claim 7, in which the two or more parts of the casing are hinged together. 9. An apparatus according to any one of claims 2 to 8, in which the casing contains sealing material, preferably gel, which sealingly encapsulates said part of the flexible envelope and said exit of the or each electrical conductor out of the envelope. 10. An apparatus according to any preceding claim, further comprising an outer box which, at least in use, contains the circuit board, the flexible envelope, and preferably also the electrical connector.

Inventors: BUEKERS VALERE, DELVAUX ROGER, DIDDENS DIRK, ERREYGERS JAN, VAN LEEUW LUC, BUEKERS, VALERE, DELVAUX, ROGER, DIDDENS, DIRK, ERREYGERS, JAN, VAN LEEUW, LUC
Applicants: BUEKERS VALERE, DELVAUX ROGER, DIDDENS DIRK, ERREYGERS JAN, LEEUW LUC VAN, RAYCHEM LTD, RAYCHEM SA NV, BUEKERS, VALERE, DELVAUX, ROGER, DIDDENS, DIRK, ERREYGERS, JAN, N.V. RAYCHEM S.A., RAYCHEM LIMITED, VAN LEEUW, LUC
Application year: 1996
Main classification: H05K5
IPC codes: H05K3, H05K5, H05K7