FR2787245A1 - CONNECTOR WITH PRESTRESSED CONTACTS AND ITS USE - Google Patents

Abstract

In order to increase the precision in the definition of a contact by pressure between a connector (1), designed to be surface-mounted, and a chip card, the connector is provided with a support plane on a plane printed circuit. This support plane is obtained by means of prestresses obtained on conductive elastic tabs (3-8) of the connector. This prestress consists in placing one end (11-13) of the conductive elastic tabs against stops (14-17) aligned in a plane. This improvement induces an ease of implementation of a connector of this kind as well as the possibility of having a statistical control of the quality of the connectors thus made.

Description

Connector with pretensioned contacts and its use

  invention relates to a connector with pre-stressed contacts and its use. Such a connector comprises elastic conductive strips provided with soldering contact tails, and an insulating structure in which the elastic conductive strips bear. It finds more particularly its use in the mounting of connectors on a printed circuit, in particular in the mounting on the surface of connectors intended to ensure an electrical connection between microcircuits of a smart card and electronic systems. These electronic systems are, in a preferred example, those of smart card readers or mobile phones. This type of connector comprises elastic conductive strips intended to ensure electrical contacts by pressure with metal surfaces or contact pads present on the chip card. Furthermore, the contact between the solder contact pins of the connector and the surface of the printed circuit on which these tails are to be soldered must be a flat contact. The advantage of the invention lies in improving the coplanarity of the electrical contact between any contact tail to be welded and the surface of the circuit.

printed.

  Connectors for surface mounting currently manufactured have solder contact tails, one end of which

  free is arched to form a contact plane with the printed circuit.

  Each contact tail to be welded defines a local contact plane intended to come into contact with the printed circuit. Taking into account all the local contact planes defines a distribution, in the thickness direction, of the contacts of the connector relative to the plane of the printed circuit. Indeed, during the manufacture of a connector, the bending of the elastic conductive strips is carried out according to methods which do not allow easily obtaining good repeatability as regards the coplanarity of the contact tails to be welded (surface mounting ). That is to say that between two elastic conductive strips there may be differences in shape and / or appreciable dimensions. On the one hand, a contact tail to be welded to a blade may not be perfectly flat. On the other hand, two contact tails to be welded, each being able to be planar, can have contact planes

  different and / or not parallel to each other.

  This type of connector then presents problems.

  Generally, this type of connector is composed of a thermoplastic insulating structure and a number of bronze contacts, six in one example. These contacts are treated and receive a triple coating, of Nickel, then tin-lead and finally a thin layer of gold for the part in contact with a smart card. The tails of these contacts are intended to be surface mounted on a printed circuit. However, in this type of embodiment, it is advisable that, during the use of the product, mounting on the surface of the connector, as well as throughout the life of the device on which it is mounted, and this sometimes under severe handling conditions. , All of the connector contacts can provide pressure

  sufficient contact for good electrical transmission.

  Indeed, a smart card connector belonging, for example, to a mobile phone or to any other electronic system which may be subjected to vibrations, will transmit these vibrations to the smart card as well as to the connector. In this case, a drop in the contact pressure on the smart card is problematic because if a vibration is too strong a contact between the smart card and the connector can be interrupted or defective, even for a short time, which can cause reading errors or

  writing information to the smart card.

  Thus it has been found that for the contact with the smart card to be considered satisfactory, it is necessary that the support plane of the contact tails to be welded to the connector is coincident or at least almost coincident with the contact plane of the printed circuit. In fact, this coplanarity also makes it possible to respond effectively to a so-called coplanarity requirement, necessary for the implementation of the method for surface mounting, CMS, a requirement which implies that any contact must be inside. a maximum tolerance interval, which is desired to be low, relative to the support plane of the contact pins to be soldered from the connector on the printed circuit, support plane which defines a reference plane for the

so-called coplanarity.

  In addition, the size constraints of the connector do not allow sufficiently precise guiding of the contact tails to be welded. All this implies that this support plan cannot obviously be determined in a precise and reproducible manner and that thus a significant dispersion in

to coplanarity is driven.

  More specifically, to ensure effective SMD welding, component outlets, that is to say the contact tails to be welded, must be designed to guarantee a coplanarity of less than 0.1 mm. This translates in reality by a dimension X, representing a distance between the bearing face of the insulation of the component and the face to be welded outlets

  CMS, whose tolerance interval is 0.1 mm (X + 0.05 mm).

  This dimension X results from a double bending of an elastic conductive strip (the area of contact with the chip card must be elastic) and it is the elasticity of this elastic conductive strip which is the cause of the

  most of the problems encountered, in particular those defined above.

  This elasticity varies according to the material used to produce an elastic conductive strip, its thickness, or even the surface treatment applied. Thus, too many quantities influence to ensure the production in large series of elastic conductive strips with a lower tolerance.

more or less 0.05 millimeter.

  In addition, this problem leads to another problem. Indeed, knowing that the coplanarity of the printed circuit with the contact plane has a high probability of being imperfect, it is necessary to carry out a check of each connector. In addition to the scrap caused, this unit check is all the longer as the number of connectors is large, which creates a loss of

  time and therefore an increase in the overall cost of such a connector.

  The object of the present invention is to remedy the problems cited by proposing a connector comprising an insulating structure and a plurality of elastic conductive strips, held in this structure, each strip being provided with a contact tail to be welded. The insulating structure has stops aligned in a plane. The contact tails to be welded press on these stops in this plane by the effect of a preload applied to them. Thus, the contact surface of the contact tails to be welded is found pressed against the plane of the stops, with a precision of the order of 0.02 mm, knowing that it is known to mold insulators with such precision. Therefore, the contact between the contact tails to be welded

  connector and the surface of the printed circuit is a perfectly flat contact.

  Thus, the contact zones of the elastic blades with the smart card are also found in a plane perfectly parallel to the contact plane of the

Smartcard.

  The invention therefore relates to a connector comprising an insulating structure and a plurality of elastic conductive strips, held in this insulating structure, each elastic conductive strip being provided with a contact tail to be welded, characterized in that the contact tails to be welded are pre-stressed and that the insulating structure has stops aligned in a plane on which press the pre-stressed contact tails.

  The invention will be better understood on reading the description which follows

  and examining the accompanying figures. These are presented for information only and in no way limit the invention. The figures show: - Figure 1: a view of the connector according to the invention; - Figure 2: a view of an elastic conductive strip of the connector according to the invention; - Figure 3: a view of an anchor plate of the elastic conductive strip with its two lateral arms;

  - Figure 4: a sectional view of the connector according to the invention.

  Figure 1 shows a connector 1 according to the invention. This connector 1 comprises an insulating structure 2, and, in a preferred example, six elastic conductive strips 3 to 8. They are distributed in groups of three, symmetrically and regularly, along two sides 9 and 10 of the insulating structure 2, these two sides 9 and 10 being opposite. Then we

  will limit the description to the elements located on side 9, the elements on side 10

  are deduced from side 9 by symmetry.

  The elastic conductive strips 3, 4, 5 respectively are provided with soldering contact tails 11, 12, 13 respectively. In a preferred example, these contact tails to be welded are in the form of flat plates and situated at the first ends of the blades 3, 4 and 5 respectively. In addition, these solder contact tails 11, 12 and 13 are arranged perpendicular to the side 9 of the insulating structure 2. In addition the insulating structure 2 has stops 14, 15, 16 and 17 regularly aligned in a plane. This plane is perpendicular to the side 9. The contact tails to be welded 11, 12, 13 have a widening in the shape of a "T". These T-shaped enlargements, coming from the contact tails to be welded 11, 12, 13, are supported under the stops 14, 15, 16 and 17. To do this, each contact tail to be welded is located between two stops. In a preferred example, the stops 14 to 17 are structures rising perpendicular to the side 9 and having at least one planar face. These flat faces are those under which the contact tails to be welded support. These stops are rigid so that pressures applied by contact tails to be welded are insufficient to deform the bearing planes of the stops. Thus, the enlargements of the contact tail to be welded 11 are supported on two stops 14 and 15, the contact tail to be welded 12 is supported on two stops 15 and 16 and so on. The plan of the stops 14 to 17

  is by design (molding) obtained within the desired tolerance.

  Figure 2 shows the elastic conductive strip 3 outside the connector

  1. It comprises an anchor plate 18 placed in the intermediate position.

  This intermediate position is a position in which the anchor plate 18 is closer to the end comprising the contact tail to be welded 11 than to the other end of the elastic conductive strip 3. This anchor plate 18 is inserted in force in a housing 19 provided for this purpose in the insulating structure 2. Thus the insulating structure 2 comprises as many housings as elastic conductive strips. In the example

  shown, the insulating structure 2 therefore comprises six housings 19 to 24.

  This forceful insertion of the anchor plate 18 ensures a fixed connection between the anchor plate 18 and the insulating structure 2. This

  anchor plate 18 projects laterally with two lateral arms 25 and 26.

  The forced insertion of the anchor plate 18 into the housing 19 provided for this purpose in the insulating structure 2 has the effect of inserting the two lateral arms 25 and 26 into two lateral grooves made in each housing. The contact tail 11 is prestressed so as to come

  press on the stops 14 and 15 once the blade has been inserted.

  This opposition of the stops 14 and 15 therefore induces maintenance of a deformation of the elastic conductive strip 3 which, while being permanent, remains an elastic deformation. Prestressing ensures contact of the contact tail to be welded 11 on the stops 14 and 15. In the connector of the invention, these are the stops 14, 15, 16 and 17 on the side 9 of the insulating structure 2 which oppose the reaction forces applied by the

  solder contact shanks 11, 12 and 13.

  The insulating structure 2 is obtained, in a preferred example, by molding. The molding methods currently used make it possible to obtain flat surfaces and dimensions with an accuracy of the order of 0.02 mm. That is to say, one can obtain surfaces whose variations in relief are contained in a space whose thickness can

  be reduced to around 0.02mm.

  The elastic properties of the blades are then used. In fact, when the contact tails to be welded are pressed against the stops, the reaction force is sufficient to obtain a deformation of the contact tails to be welded in such a way that contact between a contact tail to be welded and a stop be flat. Thus, the flatness obtained in the case of the invention for the contact tails to be welded 11, 12 and 13, is greater than the

  flatness obtained in the state of the art.

  FIG. 3 shows the anchoring plate 18 provided with two lateral arms 25 and 26. The two fixing arms 25 and 26 are extended, parallel to a plane passing through the anchoring plate 18, by two lateral fixing lugs 27 and 28 respectively. A lateral fixing lug 27 or 28 has a harpoon shape, a first flank 29 or 30 of which is perpendicular to one end 31 or 32 of a lateral arm 25 or 26 respectively. A second flank 33 or 34 is oblique with respect to the end 31 or 32 respectively. The pins 27 and 28 are arranged in such a way that, relative to a direction of insertion of the anchoring plate 18, it is the oblique sides 33 and 34 of the pins 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. The sides 29 and 30 of the

  pins 27 and 28 enter second.

  At the start of the insertion of the lateral arms 25 and 26 into the grooves 35 and 36, the pins 27 and 28 penetrate into the walls 40 and 41 of the grooves 35 and 36 respectively opposite. Thus the two pins 27 and 28 deform the walls 40 and 41 under the effect of an insertion force applied to the anchoring plate 18. This deformation of the walls 40 and 41 has the effect of producing a compressive stress on the pins 27 and 28 and therefore to fix the anchor plate 18. At the end of insertion the anchor plate 18 comes into abutment on walls 42 and 43 constituting a termination of the grooves 35 and 36 respectively. In this state, the anchor plate 18 can no longer advance because of the walls 42 and 43, nor move laterally because of the compression stresses applied by the walls 40 and 41 and neither go backwards this because of the perpendicular flanks 29 and 30 pins 25 and 26 which oppose any translational movement in this direction of

the anchor plate 18.

  The anchor plate 18 is therefore fixed and has no degree of freedom. In addition, two front corners 44 and 45 of the anchor plate 18 are bevelled. These two corners 44 and 45 are the angles which are formed by the ends 31 and 32 of the 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 the anchoring plate 18, come into contact with the walls 42 and 43 of the grooves and 36 respectively. These bevelled corners 39 and 40 make it possible to promote the engagement of the anchor 19 in the grooves 35 and 36

respectively.

  Figure 4 shows a section of the connector 1 along a section plane passing through the elastic conductive strips 3 and 8 (the elastic conductive strip 8 not being shown). In a preferred example, a housing 19 receiving the conductive strip 3 has a first opening on the side 9 of the insulating structure 2, as well as a second opening on a side 48 perpendicular to the side 9 but parallel to the plane of

contact of the stops.

  Thus, the elastic conductive strip 3, introduced by the side 9 is compressed in the housing 19. For this, the elastic conductive strip 3 has a folded shape and has a second end 49 which is in a parallel plane, but not confused, in the plane passing through the anchor plate 18. A part of the elastic conductive strip 3, located between the end 49 and the anchor plate 18, is arched so that a piece of this part opens out from the second opening on the side 48, with a donkey shape 50. It is this portion of the elastic conductive strip 3 which is intended to make electrical contact between the chip card and the connector 1. This contact area of the back donkey 50 with smart card

  is movable relative to the anchor plate.

  Thus, this arched shape of this part of the elastic conductive strip 3 allows, when an applied pressure, along an axis perpendicular to the side 48, to obtain a spring effect from this part. This spring effect ensures, in a preferred example, an electrical contact by pressure between the elastic conductive strip 3 and a metal contact pad on the chip card. In addition, the end 49 of the elastic conductive strip 3 is subjected to a second prestress. For this, it is maintained, by stops between walls 37 and 38 of the housing 19, at a height such that a distance between a stop 51, produced in the wall 38, and the plane passing through the anchoring plate 18 is less than the difference between this same plane and the end 49, when it is not subjected to any stress. The end 49 can therefore only move in a housing 52 in one direction, that facing the stop 51. A T-shaped widening of the end 49 of the elastic conductive strip 3 makes it possible to bear on this stop 51 The purpose of this latter prestressing is in particular to ensure approximately the same contact plane for all the contact zones, this contact plane being parallel to the contact plane of the contact tails to be welded. The distance between a vertex 53 of the donkey and the side 48 is such that a depression of the donkey 50 in the housing 19, due to a pressure applied by the smart card during the

  connection, always leaves at least the end 53 out of the housing 19.

  Thus, the resulting reaction force ensures sufficient plating of the contact areas of the connector 1 on the contact pads of the smart card to

  have electrical contact by pressure according to the criteria set out above.

  When inserting an elastic conductive strip 3 into the housing 19 of the insulating structure 2, it is necessary to exert a pinch between the anchoring plate 18 and the end 49. This allows the end 49 to be inserted into the housing 52. After the clamping force is released, the end 49 abuts on the stop 51. In addition, during insertion, the contact tail 11 of the elastic conductive blade 3 is placed as defined above. . In this case, the elastic conductive strip 3 is subjected to two prestresses in reaction with the anchor plate 18. The first prestress is that of the contact tails to be welded 11, 12 and 13 on the stops 14, 15, 16 and 17 In the example, two stops are used to make a prestress on a contact tail to be welded. Thus each contact tail to be welded is located between two stops. One consequence of this placement of the contact tails to be welded between the stops is that the blades are no longer mobile. We limit the risks

  for attaching a fixing blade during mounting operations.

  The insulating structure 2 is produced, in a preferred example, from a molding using a thermoplastic insulating material. Such materials have elasticity and deformation properties used in particular during the insertion of the anchors of the conductive elastic strips as explained above. The elastic conductive strips 3 to 8 are, in a preferred example, made of bronze, bronze being a material

  elastic and easy to form. That is, it can be easily deformed.

  This is one of the aims sought when the contact blades bear on the stops of the insulating structure. The contact blades thus follow the relief from the stops. In addition, the donkey structure of an elastic conductive strip, and ensuring contact with a smart card, is covered with nickel, a tin-lead alloy and / or gold in order to improve the contact characteristics of the elastic conductive strip and thus promote good electrical contact between the connector 1 and a

Smartcard.

  It should also be noted that, in general, the contact tails of the CMS outputs are easily deformable and that, consequently, the stop also ensures the protection of said tails during any manipulation.

Claims (8)

  1 - Connector (1) comprising an insulating structure (2) and a plurality of elastic conductive strips (3, 4, 5, 6, 7, 8), held in this insulating structure (2), each elastic conductive strip being provided with '' a solder contact tail (11), characterized in that the solder contact tails (11, 12, 13) are prestressed and that the insulating structure (2) has stops (14, 15, 16, 17) aligned in a plane on   which press the pre-stressed contact tails (11, 12, 13).   2 - Connector according to claim 1, characterized in that the contact tails to be welded are in the form of flat plates and located at   of the first ends of the blades.   3 - Connector according to claim 2, characterized in that the contact tails to be welded under abutment supports have a T-shaped widening.   4 - Connector according to one of claims 1 to 3, characterized in that   that the elastic conductive strips are additionally provided with a plate   anchor (18) placed in an intermediate position in the insulating structure (2).   - Connector according to claim 4, characterized in that the anchoring plate comprises lateral fixing lugs (27, 28) on the insulating structure, and in that the two lateral lugs (44, 45) of this anchor plate are beveled.   6 - Connector according to one of claims 1 to 5, characterized in that   that the elastic conductive strips have a curved shape and are compressed in housings (19-24) of the insulating structure, a second end (49) of the elastic conductive strips being subjected to   a second prestress in the housing of the insulating structure.   7 - Connector according to claim 6, characterized in that the elastic conductive strips have a width equal to a slot for passage of the housing and a second T-shaped end taking support on   edges of this passage slot.   8 - Connector according to one of claims 1 to 7, characterized in that   that the elastic conductive strips are made of bronze, in that the contact zones are covered with nickel, a tin-lead alloy and gold,   and that the insulating structure is made from a thermoplastic insulator.   9 - Use of the connector according to one of claims 1 to 8 for   its surface mounting, by solder contact tails, on a printed circuit. 1 -T