DOUBLE ADHERENT ELECTRICALLY CONDUCTIVE TAPE

Abstract: Double adherent, electrically conductive tape comprising an elastic and flexible tape (1) being adherent on both sides, and an electrically conductive material applied along at least one edge of the tape. The electrically conductive material is in the shape of at least one continuous strip (2) folded in the longitudinal direction of the tape about an edge of the tape.

Description: DOUBLE ADHERENT ELECTRICALLY CONDUCTIVE TAPE The present invention concerns a double adherent, electrically conductive tape comprising an elastic and flexible tape being adherent on both sides, and an electrically conductive material applied along at least one edge of the tape. Such a tape is previously known (e.g. of the kind marketed by 3M under the designation 3M 7303 ZAF) and may be used, e.g., to connect flexible printed circuits with circuit cards or to keep tape connected metal parts at the same electrical potential. Similar applications are found in a number of industrial connections, for instance in mobile phones and m electrically shielded apparatus cabinets. In prior arts tapes of this kind the electrically conductive material comprises small powder shaped particles mixed as an additive into the material constituting the tape itself. In order to obtain good electrical conductivity between both sides of the tape, the denseness of the metal particles must be relatively great, such that the different particles contact each other and ensure electric conduction across the tape (but not always in the longitudinal direction of the tape) . However, the adhering capacity of the tape is substantially deteriorated by metal particles mixed into the tape material with relatively great particle denseness. Without being a tape of the kind here referred to, this problem is solved according to US-A-4, 666, 547 by a two-sidedly adherent, electrically conductive bond between two metallic objects, a central main portion of the area of the bond being only adherent, while its edge portions have been made conductive by mixing of metal particles into the bonding material. In the light of this background it is an object of the present invention to provide a double adherent, electrically conductive tape that, while maintaining a good adherence capability, ensures a better electrical conductivity between both sides of the tape than conductive particles mixed into the tape material. Further objects are to provide such a tape that is of simple structure and is relatively easy and economical to manufacture. A further object of the present invention is to provide such a tape that, not withstanding the good electrical conductivity and good adherence ability at both sides, has a good flexibility and elasticity. The main object stated is achieved according to present invention in that the electrically conductive material is in the form of at least one continuous strip folded in the longitudinal direction of the tape about en edge of the tape being adherent on both sides. The good adherence is maintained in that the major portion of the tape is left free. Nonetheless, a very good electrical conductivity can be obtained between both sides of the tape in that the folded strip is continuous and has a good electrical conductivity, even if the strip is relatively thin. Thus, the electrically conductive strip may comprise a metal strip having a thickness of 10 - 500 μm. In using such a thin metal strip, for instance of a soft metal as Cu, the tape can maintain is elasticity and flexibility. The tape can easily be wound as a reel if one side of the tape is coated with a non-adhering protective foil. If so desired or required an electrically conductive strip may of course be applied at both edges of the tape. As mentioned above the electrically conductive tape suitably has a somewhat less thickness than the tape. Favourably, the strip can be folded and pressed into the material of the tape such that the outer side of the strip is substantially flush with the free part of the tape on both sides of the tape. Hereby the tape can be used m the normal way for a double adhesive tape, and, further, winding of the tape to a reel is facilitated. To ensure a good adhesiveness of the tape, the folded strip should cover an edge portion forming only a minor part of the entire width of the tape. Relations between the width of the edge portion and the entire width of the tape suitably amount to 0, 01 - 0, 5. Further convenient features and advantages of the invention appear from the following detailed description of the preferred embodiment. Accordingly, the present invention is more closely explained hereinafter, reference being made to the accompanying drawing showing a double adherent, electrically conductive tape according to the present invention. Fig. 1 shows schematically a perspective view of a tape according to the invention wound to a reel; Fig. 2 shows a cross section through the tape according to Fig. 1; and Fig. 3 shows a modified embodiment of the tape according to the invention. The tape according to the present invention shown m Figs. 1 and 2 comprises substantially a homogenous tape 1 including an elastic and flexible material having adherent properties, for instance of acrylic type, and a relatively thin, continuous electrically conductive strip 2 folded about an edge of the tape 1. The tape 1 has a substantially rectangular cross section having a width of 5 - 200 mm and a thickness of 0,1 - 5 mm. Of course the width is substantially greater that the thickness. Preferably, the width is 8 - 100 mm and the thickness 0,5 - 2 mm. As mentioned, the folded strip 2 has a substantially less thickness, viz. 10 - 500 μm, preferably 20 - 100 μm, and preferably comprises a thin strip of metal having good electrical conductivity, for instance copper, silver or gold or, if the requirements of electric conductivity are not high, aluminium. Due to the tape 1 being flexible and elastic the metal strip can easily be folded under certain compression of the material of the tape 1, such that the upper and lower legs 2a, 2b of the strip are substantially flush with the free upper and lower surfaces, respectively, of the tape. Hereby, the winding of the tape on a reel is facilitated, preferably with a non-adhering protecting foil 3, as shown in Fig. 1, and, further, the normal use of the tape is facilitated. Consequently, a good contact is ensured against mutually plane parallel surfaces of objects to be interconnected by means of the tape. The simplest manner is to fold the electrically conductive strip 2 symmetrically about the edge of the tape 1, such that the upper and lower legs 2a, 2b become equally long. If desired, for instance in order to ensure a larger contact surface on one side, it is conceivable to let one leg 2a or 2b be larger than the other one. When interconnecting two components by means of a double adherent tape, a certain press power is normally applied such that the tape is brought to good contact with the surfaces of the components even in case of possible unevenness. It is realised that good electric contact is hereby obtained between the legs 2a, 2b of the electrically conductive strip and the respective component. The variant shown in Fig. 3 differs from the embodiment of Figs. 1 and 2 only in that an electrically conductive strip 2 is applied at each edge of the tape 1. Such a tape becomes somewhat more expensive to manufacture, but due to the symmetry its winding is facilitated, and the electrical conductivity between the opposed sides becomes even better. The invention can be realised in different manners within the scope of the inventive idea stated in claim 1. For instance, the tape 1 may comprise a multi-layer structure, for instance having a central carrying layer and opposed adhesive layers. In the embodiment according to Fig. 3 it is further possible, in order to obtain increased strength and electrical conductivity between both sides of the tape, to apply metal threads or strips around the entire tape at relatively large mutual distances. Such strips or threads may be regularly spaced as crosswise directed encircling flattened rings or in flattened helical shape along the tape. Of course, the materials of the tape 1 and the electrically conductive strip 2 may be chosen according to the wish of the skilled person in view of the required properties of the tape in specific applications. It is evident that a tape according to the present invention offers conductive properties not only across the tape, but also in its longitudinal direction, that are superior to those of a tape having electrically conductive particles mixed into its material.

Claims: C L A I M S 1. The present invention concerns a double adherent, electrically conductive tape comprising an elastic and flexible tape being adherent on both sides, and an electrically conductive material applied along at least one edge of the tape, c h a r a c t e r i z e d i n that the electrically conductive material has the shape of at least one continuos strip (2) folded in the longitudinal direction of the tape about and edge of the tape (1) . 2. Tape according to claim 1, c h a r a c t e r i z e d i n that said strip (2) has substantially less thickness than the tape (1 ) . 3. Tape according to claim 2, c h a r a c t e r i z e d i n that said continuos strip (2) is pressed into an edge portion of the tape (1), such that the outer side of the strip is substantially flush with the free portion of the tape on both sides of the tape. 4. Tape according to claim 1 - 3, c h a r a c t e r i z e d i n that on both sides of the tape the folded strip (2) covers an edge portion forming a minor part of the entire width of the tape (1) . 5. Tape according to claim 4, c h a r a c t e r i z e d i n that on both sides of the tape the ratio between the width of the edge portion and the entire width of the tape amounts to 0,01 - 0,5. 6. Tape according to anyone of the preceding claims, c h a r a c t e r i z e d i n that the thickness of the tape is 0, 1 - 5 mm and its width is 5 - 200 mm. 7. Tape according to claim 6, c h a r a c t e r i z e d i n that the thickness of the tape is 0,5 - 2 mm and its width is 8 - 100 mm. 8. Tape according to anyone of the preceding claims, c h a r a c t e r i z e d i n that said strip comprises of a thin strip (2) of metal having a good electrical conductivity. 9. Tape according to claim 8, c h a r a c t e r i z e d i n that the metal strip (2) has a thickness of 10-500 μm preferably 20-100 μm. 10. Tape according to any one of the preceding claims, c h a r a c t e r i z e d i n that two electrically conductive strips (2) are folded about one edge each of the tape (1) .

Inventors: OESTERHOLM OLOV, OESTERHOLM, OLOV
Applicants: FLEXMAN AB, OESTERHOLM OLOV, OESTERHOLM, OLOV
Application year: 1999
Main classification: H01R4
IPC codes: H01B5, H01R4, H05K3