Abstract:
In order to increase the precision of the definition of a contact by pressure between a connector ( 1 ), designed to be surface-mounted, and a smart card, one assures a support plane for the connector, this latter on a flat printed circuit. This support plane is created by means of vertical prestresses on elastic conductive strips ( 3, 4, 5, 6, 7, 8 ) of the connector. This vertical prestress consists of pressing one end ( 11, 12, 13 ) of the elastic conductive strips onto fixed pieces ( 14, 15, 16, 17 ) aligned in a plane. This improvement makes such a connector easy to use and makes it possible to have a statistical inspection of the quality of the connectors thus made.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of application Ser. No. 09/455,585, filed Dec. 6, 1999 and titled: “CONNECTOR WITH PRESTRESSED CONTACTS AND ITS USE” 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    I. Field of the Invention  
           [0003]    The present invention relates to a connector with prestressed contacts and its use, and more particularly to a connector having vertically prestressed contacts. A connector in accordance with the features of the present invention has elastic conductive strips provided with contact pins that are to be soldered, and an insulating structure in which the elastic conductive strips are supported. The invention particularly finds application in mounting connectors on a printed circuit board (PCB), such as, for example, in the surface mounting of connectors designed to assure an electrical connection between microcircuits of a smart card and of electronic systems. These electronic systems are, in a preferred example, those of smart card readers or mobile telephones. This type of connector has elastic conductive strips designed to assure electrical contacts by pressure with metallic surfaces or contact areas present on the smart card. Moreover, the contact between the connectors contact pins that are to be soldered and the surface of the printed circuit on which these pins must be soldered, must be a flat contact. The invention also relates to an improvement in the coplaneity [inherent flatness] of the electrical contact between any contact pin that is to be soldered and the surface of the printed circuit. In accordance with the features of the present invention a coplaneity of less than 0.02 mm is obtained by vertically prestressing each contact pin that is to be soldered.  
           [0004]    II. Description of the Prior Art  
           [0005]    Connectors designed for surface mounting that are currently manufactured have contact pins that cure to be soldered. One free end of the pin is chamfered to form a contact plane with the printed circuit. Each contact pin that is to be soldered defines a local contact plane designed to come into contact with the printed circuit. Taking into account all the planes of local contact defines a distribution, in the direction of the thickness, of connector contacts with regard to the plane of the printed circuit. In fact, during the manufacture of a connector, the chamfering of the elastic conductive strips is produced according to processes which do not easily permit obtaining a good repeatability with regard to the coplaneity of the contact pins to be soldered (surface mounting). Thus, appreciable differences of form and/or dimensions may exist between two elastic conductive strips. On the one hand, one contact pin of a strip that is to be soldered may not be perfectly planar. On the other hand, two contact pins that are to be soldered, each one of which may be planar, may have different contact planes and/or contact planes that are not parallel to one another. This type of connector thus presents problems.  
           [0006]    In a general manner, the connector described above is comprised of a thermoplastic insulating structure and a certain number of bronze contacts; e.g. six in one example. These contacts are treated and receive a triple coating of nickel, then tin-lead, and finally a layer of gold for the part in contact with a smart card. The pins of these contacts are designed to be surface-mounted on a printed circuit board. In this type of design, the contact assembly of the connector must adequately assure a sufficient contact pressure for good electrical transmission.  
           [0007]    In fact, a smart card connector, for example, belonging to a mobile telephone or any other electronic system likely to be subjected to vibrations, will transmit these vibrations to the smart card as well as to the connector. In this case, a lowering of the contact pressure on the smart card is problematic, since, if a vibration is too strong, a contact between the smart card and the connector can be interrupted or defective, even for a brief instant, which can lead to reading or writing errors of data in the smart card.  
           [0008]    Thus, in order for there to be a satisfactory contact with a smart card, it is necessary that the support plane of the connector&#39;s contact pins that are to be soldered be merged or at least quasi-merged with the contact plane of the printed circuit. This “coplanarity” permits effectively conforming to a requirement called coplaneity [inherent flatness] necessary for implementing the process for surface mounting, (i.e.,CMS), a requirement that implies that any contact must be found within a maximum tolerance range, which is desirably small, relative to a support plane of the connector&#39;s contact pins that are to be soldered on the printed circuit, a support plane that defines a reference plane for the coplaneity.  
           [0009]    Furthermore, the size constraints of the connector do not permit a sufficiently precise guidance of the contact pins that are to be soldered. This implies that the support plane cannot be determined in a precise and reproducible manner and therefore, a significant dispersion with regard to coplaneity is brought about.  
           [0010]    More precisely, in order to assure an effective CMS soldering, the outlets of the components, i.e., the contact pins that are to be soldered, must be designed to permit guaranteeing a coplaneity of less than 0.1 mm. This is translated into reality by a dimension X, representing a distance between the support face of the insulator of the component and the face to be soldered of the CMS outlets, whose tolerance range is 0.1 mm (X±0.05 mm).  
           [0011]    This dimension X results from a double chamfering of an elastic conductive strip (the contact zone with the smart card must be elastic) and it is the elasticity of this elastic conductive strip which is the cause of most of the problems encountered as defined above. This elasticity varies as a function of the material used to create an elastic conductive strip, its thickness, or even the surface treatment applied. Thus, there are too many influences to assure obtaining, by mass production, elastic conductive strips with a tolerance of less than approximately 0.05 millimeter.  
           [0012]    Moreover, this problem leads to another problem. In fact, knowing that the coplaneity of the printed circuit with the contact plane has a high probability of being imperfect provides for the need for each connector to be inspected. In addition to the number of rejections this entails, this piece-by-piece inspection is as lengthy as the number of connectors is large, which creates a loss of time. This results in an increase in the overall cost of such a connector.  
         SUMMARY OF THE INVENTION  
         [0013]    A primary objective of the present invention is to remedy the problems cited by proposing a connector having an insulating structure and a multiple number of elastic conductive strips, held in this structure, each strip being provided with a contact pin that is to be soldered. The insulating structure has fixed pieces aligned in a plane. The contact pins that are to be soldered are supported on these fixed pieces in this plane by the effect of a vertical prestress that is applied to them. Thus, the contact surface of the contact pins that are to be soldered is found pressed into the plane of the fixed pieces, with a precision of the order of 0.02 mm, given that molding of insulators with such precision is known. As a result of this, the contact between the connector&#39;s contact pins that are to be soldered and the printed circuit board surface is a perfectly flat contact. Thus, the contact zones of the elastic strips with the smart card is also found in a plane perfectly parallel to the contact plane of the smart card.  
           [0014]    The invention therefore concerns a connector having an insulating structure and a multiple number of elastic conductive strips, held in this insulating structure, each elastic conductive strip being provided with a contact pin to be soldered, wherein the contact pins that are to be soldered are vertically prestressed and that the insulating structure has fixed pieces aligned in a plane on which the prestressed contact pins press.  
           [0015]    In accordance with the preferred features of the present invention a connector includes an insulating structure and a plurality of elastic conductive strips, each of the strips having a first lower end portion forming a contact pin and a second upper end portion and each strip being positioned within the insulating structure. Each contact pin is adapted to be soldered to a surface, and each contact pin being vertically prestressed, thereby resulting in coplaneity of each contact pin that is to be soldered, the insulating structure including fixed pieces aligned in a single plane and adapted to press the vertically prestressed contact pins into contact with the surface thereof.  
           [0016]    In accordance with the features of the present invention a coplaneity of less than 0.02 mm is obtained by vertically prestressed contact pins.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The accompanying drawings, which are incorporated in and constitute a part of the specification illustrate one embodiment of the invention and, together with the description, serve to explain the principles of the invention.  
         [0018]    [0018]FIG. 1: a perspective view of the connector according to the invention;  
         [0019]    [0019]FIG. 2: a perspective view of an elastic conductive strip of the connector according to the invention;  
         [0020]    [0020]FIG. 3: a plan view of an anchoring plate of the elastic conductive strip with its two lateral arms; and  
         [0021]    [0021]FIG. 4: a sectional view of the connector according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    [0022]FIG. 1 illustrates a connector  1  according to the features of the present invention. The connector I includes an insulating structure  2  and, in one preferred example, six elastic conductive strips  3 ,  4 ,  5 ,  6 ,  7 , and  8 . The strips are distributed by groups of three, symmetrically and regularly, along the two opposite sides  9  and  10  of insulating structure  2 ,. The following description will limit the description to the elements situated on side  9 . However, the elements on side  10  can be deduced from the description of side  9  by symmetry.  
         [0023]    The conductive elastic strips  3 ,  4 ,  5 , respectively on side  9 , are provided with contact pins  11 ,  12 ,  13  on each lower end portion of each strip respectively to a printed circuit board (not shown). In one a preferred example, these contact pins that are to be soldered to a printed circuit board are in the form of flat plates and situated at a first lower end portion of each of strips  3 ,  4  and  5 , respectively. In addition, these contact pins  11 ,  12  and  13  that are to be soldered are preferably arranged perpendicularly to side  9  of insulating structure  2 . In addition, insulating structure  2  includes fixed pieces  14 ,  15 ,  16  and  17  regularly aligned in a plane. This plane is preferably perpendicular to side  9 . The contact pins  11 ,  12 ,  13  that are to be soldered have a generally “T”-shaped widening configuration. These T-shaped widenings, are derived from contact pins  11 ,  12 ,  13  being supported under fixed pieces  14 ,  15 ,  16  and  17  in the manner illustrated in FIG. 1. To accomplish this configuration, each contact pin  11 ,  12 ,  13  is situated between two fixed elements  14 - 15 ,  15 - 16 , and  16 - 17  respectively. In one preferred example, fixed elements  14 , 15 , 16  and  17  are structures rising perpendicularly to side  9  and have at least one flat face. These flat faces are those under which the contact pins  11 , 12  and  13  are supported. These fixed elements are substantially rigid, so that the pressures applied by the contact pins that are to be soldered are insufficient to deform the support planes of the fixed elements  14 ,  15 ,  16  and  17 . Thus, the widenings  11 A and  11 B of the contact pin  11  are supported by two fixed elements  14  and  15  and the widenings  12 A and  12 B of contact pin  12  is supported by two fixed pieces  15  and  16  and so on. The plane of fixed pieces  14 ,  15 ,  16  and  17  is by design (molding) obtained within the tolerance sought.  
         [0024]    [0024]FIG. 2 illustrates conductive elastic strip  3  in a position removed from connector  1 . Strip  3  includes an anchoring plate  18  placed in an intermediate position. This intermediate position is a position in which anchoring plate  18  is closer to the end of strip  3  with contact pin  11 . Anchoring plate  18  (see FIG. 1) is forcefully inserted into opening  19  positioned in insulating structure  2 . Insulating structure  2  also has openings for the other elastic conductive strips  4 ,  5 ,  6 ,  7  and  8 . In the example shown, insulating structure  2 , therefore, has six openings  19  to  24 . The forceful insertion of anchoring plate  18  into housing  2  permits assuring a fixed bond between anchoring plate  18  and insulating structure (housing)  2 . Anchoring plate  18  projects laterally having two lateral arms  25  and  26 . The forceful insertion of anchoring plate  18  into opening  19  in insulating structure  2  has the effect of inserting the two lateral arms  25  and  26  into two lateral grooves (not shown) in housing  2 .  
         [0025]    Contact pin  11  is vertically prestressed so as to be positioned to be pressed onto fixed pieces  14  and  15  once the strip  3  is inserted within housing  2 . Each contact pin is vertically prestressed against the fixed pieces by an upwardly ducted vertical force resulting from the bending of strip  3  and anchoring plate  18 . Each strip ( 3 ,  4 ,  5 ,  6 ,  7  and  8 ) comprises two opposite portions, i.e. a vertically prestressed lower portion and an upper portion. It is the lower vertically prestressed portion of each strip that is responsible for the coplaneity of less than 0.02 mm. This coplaneity is obtained by an upward vertical force that each upper surface of each contact pin ( 11 , 12  and  13 ) applies directly on shoulders  14 ,  15 ,  16  and  17  on insulting structure  2 . There is clearly a distinction between the lower portion of each strip which is vertically prestressed, and the upper portion of each strip (also prestressed against edges  51 —See FIG. 4—but not responsible for the coplaneity advantage). The prestress of the upper portion of each strip ensures a good enough degree of contact between the top portion of each strip and a PCB such as a smart card.  
         [0026]    The vertically prestressed state of each lower portion of each strip is obtained through the bending of the strip illustrated in FIG. 2 (around the inflexion zone between the contact pin  11  and the anchoring plate  18 ) when the achoring plate is placed into walls  37  and  38  of housing  39  (See FIG. 3). This results into the T shaped contact pins being pressed against the bottom of shoulders  14  to  17  and therefore the coplaneity of less than 0.02 mm.  
         [0027]    This opposition of fixed pieces  14  and  15  therefore maintains the deformation of elastic conductive strip  3 , which, while being permanent, remains an elastic deformation. The vertically prestressed condition of each lower portion of each strip permits assuring the contact of each contact pin to be soldered (e.g.  11 ) on fixed pieces (e.g.  14  and  15 ). It is fixed pieces  14 ,  15 ,  16  and  17  on side  9  of insulating structure  2  that are opposed to the reaction forces applied by contact pins  11 ,  12  and  13 .  
         [0028]    Insulating structure  2  is obtained, in a preferred example, by a molding process. The molding processes used currently permit obtaining flat surfaces and dimensions with a precision of the order of 0.02 mm (i.e., one can obtain surfaces whose relief variations are contained in a space whose thickness can be reduced to approximately 0.02 mm).  
         [0029]    In accordance with the features of the present invention the elastic properties of the strip are used. In fact, during support of the contact pins on the fixed pieces, the reaction force is sufficient to obtain a deformation of the contact pins to be soldered, so that a contact between a contact pin and a fixed piece is flat. Thus, the planeity obtained in the case of the invention for contact pins to be soldered  11 ,  12  and  13  is greater than the planeity obtained in the state of the art.  
         [0030]    [0030]FIG. 3 illustrates anchoring plate  18  provided with two lateral (attachment) arms  25  and  26 . The two attachment arms  25  and  26  are extended, in parallel to a plane passing through anchoring plate  18 , by two lateral attachment catches  27  and  28 , respectively. A lateral attachment catch  27  or  28  has a form of a harpoon or wedge, a first side  29  or  30  of which is perpendicular to an end  31  or  32  of one of lateral arms  25  or  26 , respectively. A second side  33  or  34  is oblique with regard to end  31  or  32 , respectively. Catches  27  and  28  are arranged such that, with regard to the direction of insertion of anchoring plate  18 , it is oblique sides  33  and  34  of catches  27  and  28  which first penetrate into grooves  35  and  36 , respectively, provided for this purpose in walls  37  and  38  of a housing  39 . Sides  29  and  30  of catches  27  and  28  penetrate in second place.  
         [0031]    At the beginning of insertion of lateral arms  25  and  26  into grooves  35  and  36 , catches  27  and  28  penetrate into walls  40  and  41  of grooves  35  and  36  respectively, facing one another. Thus the two catches  27  and  28  deform walls  40  and  41  under the effect of an insertion force applied to anchoring plate  18 . This deformation of walls  40  and  41  has for an effect producing a compression stress on catches  27  and  28  and therefore attaching anchoring plate  18 . At the end of insertion, anchoring plate  18  comes to abut walls  42  and  43  constituting a termination of grooves  35  and  36 , respectively. In this state, anchoring plate  18  cannot advance further because of walls  42  and  43 , nor can it laterally budge, because of the compression stresses applied by walls  40  and  41 , nor can it go backwards, because of perpendicular sides  29  and  30  of catches  27  and  28  which oppose any translation movement in this direction of anchoring plate  18 .  
         [0032]    Anchoring plate  18  is therefore fixed. In addition, the two front comers  44  and  45  of anchoring plate  18  are chamfered. These two comers  44  and  45  are the angles that are formed by ends  31  and  32  of lateral arms  25  and  26  with sides  46  and  47 , respectively. These sides  46  and  47  are those which, at the end of insertion of anchoring plate  18 , enter into contact with walls  42  and  43  of grooves  35  and  36 , respectively. These chamfered comers  44  and  45  permit favoring the engagement of anchorage  18  in grooves  35  and  36 , respectively.  
         [0033]    [0033]FIG. 4 illustrates a section of connector  1  along a sectional plane passing through elastic conductive strips  3  and  8  (conductive elastic strip  8  is not shown). In a preferred example, an opening  19  receiving conductive strip  3  has a first opening on side  9  of insulating structure  2 , as well as a second opening on a side  48  perpendicular to side  9  but parallel to the contact plane of the fixed pieces.  
         [0034]    Thus, elastic conductive strip  3 , introduced in side  9  is compressed in opening  19 . For this, conductive elastic strip  3  has a folded-back form and has a second end  49 , which is found in a parallel plane, and not merged, with the plane passing through anchoring plate  18 . A part of elastic conductive strip  3 , situated between end  49  and anchoring plate  18 , is chamfered in such a way that a piece of this part projects from the second opening of side  48 , with a saddle-back shape  50 . It is this portion of conductive elastic strip  3  which is designed to produce an electrical contact between the smart card and connector  1 . This contact zone of saddle-back shape  50  with the smart card is mobile with regard to the anchoring plate.  
         [0035]    Thus, this chamfered form of this part of elastic conductive strip  3  permits, obtaining a spring effect of a portion of this part along an axis perpendicular to side  48 , when pressure is applied. This spring effect assures, in a preferred example, an electrical contact by pressure between elastic conductive strip  3  and a metal contact area on a smart card. Moreover, end  49  of elastic conductive strip  3  is subjected to a second prestress. For this, it is held, by fixed pieces between walls  37  and  38  of housing  19 , at a height such that a deviation between a fixed piece  51 , made in wall  38 , and the plane passing through anchoring plate  18  is less than the deviation between this same plane and end  49 , when it is not subjected to any stress. End  49  can therefore only move in a housing  52  in a single direction, which is opposite fixed piece  51 . A T-shaped widening of end  49  of elastic conductive strip  3  permits taking support on this fixed piece  51 . The latter prestress has for an objective notably to assure approximately the same contact plane for all the contact zones, this contact plane being parallel to the contact plane of the contact pins to be soldered. The deviation between a peak  53  of the saddle-back and side  48  is such that a forcing of saddle-back  50  into housing  19 , resulting from pressure applied by the smart card during the connection, always leaves at least end  53  outside of housing  19 . Thus the resulting reaction force assures a sufficient pressing together of the contact zones of connector  1  on the contact areas of the smart card so as to have an electrical contact by pressure according to the criteria disclosed above.  
         [0036]    During the insertion of an elastic conductive strip  3  in opening  19  of insulating structure  2 , it is necessary to resiliently bend end  49  towards anchoring Oplate  18 . This permits end  49  to be inserted into housing  52 . After release of the bending force, end  49  comes to abut fixed piece  51 . Moreover, during insertion, contact pin  11  of elastic conductive strip  3  is placed as defined previously. In this case, elastic conductive strip  3  is subjected to two reaction prestresses with anchoring plate  18 . The first prestress is that of contact pins to be soldered  11 ,  12  and  13  on fixed pieces  14 ,  15 ,  16  and  17 . In the example, two fixed pieces are used to create a prestress on one contact pin to be soldered. Thus each contact pin to be soldered is found between two fixed pieces. A consequence of this placement of the contact pins to be soldered between the fixed pieces is that the strips are no longer mobile. Thus the risks of catching an attachment strip during the mounting operations is limited.  
         [0037]    Insulating structure  2  is made, in a preferred example, by molding an insulating thermoplastic material. Such materials have properties of elasticity and deformation used notably during insertion of the anchorings for the conductive elastic strips as explained above. Elastic conductive strips  3  to  8  are bronze, in a preferred example, bronze being an elastic and easy-to-shape material. That is to say, it can be deformed easily. This is one of the objectives sought when the contact strips come to be supported on the fixed pieces of the insulating structure. The contact strips thus mate with the relief shape formed by the fixed pieces. Moreover, the saddle-back structure of the elastic conductive strip, assuring contact with a smart card, is coated with nickel, a tin-lead alloy and/or gold, in order to improve the contact characteristics of the elastic conductive strip and thus to favor a good electrical contact between connector  1  and a smart card.  
         [0038]    It is also to be noted that, in general, the contact pins of CMS outlets are easily deformable and that, consequently, the fixed piece permits also assuring protection of said pins during any manipulation.  
         [0039]    While this invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.