Patent Publication Number: US-7589607-B2

Title: Thin contactor

Description:
The present invention relates to a contactor, of the type comprising a fixed contact plate, a moveable contact plate and means for retaining the two contact plates, which moveable contact plate is resiliently deformable between a position remote from the fixed contact plate and a position in contact with the fixed contact plate. 
   A number of miniature electronic devices require contactors of reduced size. These contactors allow an electrical circuit to be opened or closed when they are activated, and can return to the previous state thereof when they are released. 
   For specific applications, the contactors must have a thickness which is as small as possible. 
   It has been proposed that contactors be produced in which the two contact plates are retained by a casing which is over-moulded and which is produced by plastics material being injected between and around the two plates. 
   This solution is relatively difficult to implement. 
   The object of the invention is to provide a very thin contactor which can be produced in a straightforward manner. 
   To this end, the invention relates to a contactor of the above-mentioned type, characterised in that the retaining means comprise an adhesive insulating sheet which is interposed between the two contact plates, which adhesive insulating sheet adheres to each of the two contact plates along the two opposing faces thereof. 
   According to particular embodiments, the contactor comprises one or more of the following features:
         the adhesive insulating sheet is the only means which ensures that the two contact plates are retained;   the adhesive insulating sheet forms a frame which has a closed contour and which delimits a passage for the moveable contact plate in a contact position;   the two contact plates and the adhesive insulating sheet have, at the periphery thereof, contours which are substantially identical;   the adhesive insulating sheet has a thickness of between 50 microns and 150 microns;   the adhesive insulating sheet comprises an insulating support film which is covered on each face with a layer of an adhesive;   it comprises a conductive cover which is formed by a metal plate which covers one of the contact plates, and an adhesive insulating sheet is interposed between the conductive cover and the covered contact plate, which adhesive insulating sheet adheres to the contact plate and the conductive cover along the two opposing faces thereof;   the moveable contact plate comprises a resiliently deformable contact region and a connection region, the moveable contact plate being fixedly joined to the adhesive insulating sheet by means of the connection region; and   the adhesive insulating sheet is thermally activated.       

   The invention also relates to a method for producing a contactor of the type described above, characterised in that it comprises the following steps:
         stacking a fixed contact plate and a moveable contact plate, a thermally activatable adhesive insulating sheet being interposed therebetween; and   heating the stack formed in this manner in order to ensure that the adhesive insulating sheet is activated and to fixedly join the two contact plates.       

   
     The invention will be better understood from a reading of the following description, given purely by way of example and with reference to the drawings, in which: 
       FIG. 1  is an isometric perspective view of the contactor according to the invention; 
       FIG. 2  is an isometric perspective view of the contactor of  FIG. 1 ; and 
       FIG. 3  is a cross-section of the contactor according to the invention, taken along line III-III of  FIG. 1 . 
   

   The contactor  10  illustrated in the Figures is intended to be fixedly joined and connected to a printed circuit by means of welding. 
   The contactor  10  comprises four connection terminals  12 A,  12 B,  12 C and  12 D. The terminals  12 B and  12 D ensure that a protection housing for the contactor is linked, whilst the terminals  12 A,  12 C define between them a contact which can be opened or closed in accordance with the state of the contactor. 
   More precisely, and as illustrated in  FIG. 2 , the contactor substantially comprises a fixed contact plate  14  and a moveable contact plate  16 , between which an adhesive insulating sheet  18  is interposed which forms a spacer and which ensures that the two contact plates  14 ,  16  are linked. 
   The plates  14 ,  16  are formed into metal sheets having a constant thickness. This thickness is, for example, equal to 50 microns. It is preferably between 40 and 70 microns. These plates are formed from stainless steel. In one variant, the fixed contact plate  14  is formed from brass. 
   The fixed contact plate  14  is of a generally square form. This plate is completely flat with the exception of a tab which is shaped towards the outer side and which forms the connection terminal  12 A. The plate  14  forms a solid wall and has no openings on the surface thereof. 
   An insulating sheet  20  is advantageously arranged on the surface of the fixed contact plate  14  at the opposite side to the moveable contact plate  16 . It is bonded by any suitable means. The insulating sheet  20  allows electrical contact to be prevented between the fixed contact plate  14  and the tracks of the printed circuit when the contactor is installed on the printed circuit. 
   The moveable contact plate  16  is of a generally square form externally. It has a contour which is substantially identical to that of the fixed contact plate  14 . It has, in a corner opposite that where the terminal  12 A is formed, a shaped tab which forms the terminal  12 C. In the central portion thereof, the moveable contact plate  16  has, as illustrated in  FIG. 3 , a resiliently deformable bell-like member  22 . This bell-like member is rounded and generally protrudes at the opposite side to the fixed contact plate  14 . The bell-like member  22  is generally hemispherical. It is bordered at its periphery by three arcuate apertures and is connected to the peripheral portion of the moveable contact plate  16  by means of three flat connection tabs  23 . The peripheral portion of the contact plate forms a frame  24  along which the moveable contact plate is fixedly joined to the fixed contact plate by means of the adhesive sheet  18 . 
   The adhesive insulating sheet  18  is of a generally square form and has a periphery which has a shape substantially identical to that of the contact plates  14  and  16 . This sheet is flat and has a circular central opening  25  which internally forms a circular passage which allows the bell-like member  22  to be deformed in order to be brought into contact with the fixed contact plate  14 . 
   In this manner, the sheet  18  delimits a frame which forms a closed contour whose shape corresponds to that of the frame  24  of the moveable contact plate. 
   The sheet  18  has a constant thickness of between 50 microns and 150 microns. It preferably comprises an insulating intermediate support film which forms a support core which is constituted, for example, of polyester. This film has a thickness in the order of 30 microns. Each face of the film carries a layer of thermally activatable adhesive having a thickness in the order of 35 microns. 
   The sheet  18  is interposed between the contact plates  14  and  16 . It ensures that there is sufficient spacing between the two plates to ensure that they are electrically insulated and ensures that the two plates are assembled owing to the adhesion thereof. 
   Furthermore, the contactor comprises a cover or housing  26  which is attached above the assembly of the two contact plates  14  and  16 . This housing is formed by a generally flat metal plate which is shaped only in order to form two tabs which constitute the terminals  12 B,  12 D. The housing has, in the central portion thereof, an aperture  27  which allows the bell-like member  22  to be activated. 
   An adhesive insulating retaining sheet  28 , identical to that of the sheet  18 , is interposed between the moveable contact plate  16  and the housing  26 . It ensures that the housing  26  is retained and insulated relative to the moveable contact plate  16 . The sheet  28  has a central opening  29  for activating the bell-like member  22 . 
   Finally, an actuator  30 , formed by a solid insulating disc, is adhesively bonded to the top of the bell-like member  22 . This actuator  30  protrudes through the passages delimited through the adhesive sheet  28  and the housing  26 . 
   It will be appreciated that, when the actuator  30  is pressed, the bell-like member  22  resiliently deforms in a direction perpendicular to the plane of the sheet  18  in such a manner that the curvature thereof is reversed and it comes into contact with the fixed contact plate  14 . In this manner, an electrical connection is established between the terminals  12 A and  12 C. 
   When the actuator  30  is released, and under the resilient action of the bell-like member  22 , the bell-like member  22  once more assumes the rounded form thereof as illustrated in the Figures, thus opening a circuit between the terminals  12 A and  12 C. 
   It will be appreciated that the use of the adhesive insulating sheet. 18  between the two contact plates allows a very thin contactor to be readily produced, the adhesive sheet at the same time ensuring that there is insulation between the two contact plates and that they are spaced apart and retained. 
   In order to produce a contactor of this type, the film which forms the core of the sheet  18  is first coated on each of the faces thereof with a thermally activatable adhesive. After each of the metal plates and insulating sheets has been pre-cut, a stack is formed as illustrated in  FIG. 2 , the insulating sheets  18  and  28  being interposed between the contact plates and the housing  26 . 
   The stack which is formed in this manner is then heated, for example, under the action of electrical resistors which are applied to the two opposing faces of the contactor. Under the action of the heat, the thermally activatable adhesive becomes active and ensures a definitive connection between the insulating sheets and the metal plates which are in contact therewith. 
   When the heating operation is complete, the various layers of the contactor are definitively connected to each other. 
   Finally, the actuator  30  is positioned by being bonded to the top of the dome  22 . 
   In this manner, it will be appreciated that a contactor of this type can be produced in a straightforward manner.