Electrical connector with self-adjusting contact elements

An electrical connector for surface mounting and solder anchoring on a circuit board. The electrical connector has a plurality of contact elements that engage respective contact pads on the circuit board. The contact elements are free to move within the body of the electrical connector such that they can spatially self-adjust in order to compensate for non-planarity of the circuit board, as well as for mismatches between the inherent properties of the different connector and circuit board materials.

In the drawings, embodiments of the invention are illustrated by way of example. It is to be expressly understood that the description and drawings are only for purposes of illustration and as an aid to understanding, and are not intended to be a definition of the limits of the invention. 
 DETAILED DESCRIPTION FIG. 1 illustrates an electrical connector 10 constructed in accordance with a non-limiting example of implementation of the present invention. The electrical connector 10 includes two main components, notably a body of insulating material 12 and a plurality of contact elements 14 . The contact elements 14 are mounted in the body of insulating material 12 . The body of insulating material 12 is made of any suitable synthetic material that has the requisite dielectric strength and mechanical resistance characteristics. The body of insulating material 12 includes a topside 16 and a bottom side 18 , the latter constituting a circuit board facing side. The circuit board facing side 18 , which is best shown in FIG. 3 , is substantially flat. The body of insulating material 12 defines a plurality of cages 20 designed to receive respective ones of the contact elements 14 . Each cage 20 is generally rectangular in shape and includes a top wall, a bottom wall and four sidewalls. The bottom wall is provided with an aperture 22 that opens on the circuit board facing side 18 . One of the sidewalls of each cage 20 is open at 24 to allow access to the contact elements 14 mounted in the cages 20 . Each cage also has a cylindrical extension 26 at its top, opening on the topside 16 . Note that, in a variant example, the opening at 24 is only a partial opening of the respective sidewall of cage 20 . In another variant, two opposite sidewalls of each cage 20 are open, or partially open, in order to allow access to the contact element 14 therein. With reference to FIG. 2 , each contact element 14 is made of metallic material such as brass, copper or aluminum. The contact element 14 has a contact element body portion 28 having generally a rectangular shape and defining a recess 30 in which the conductor portion of a wire (not shown in the drawings) can be inserted. The top of the contact element body portion 28 is provided with a threaded aperture 32 to receive a screw 34 (shown in FIG. 1 ). As it will be plain to a person skilled in the art, the screw 34 is used to secure in place the conductor of the wire inserted in the recess 30 . Optionally, a L-shaped strip 36 (best shown in FIGS. 1 and 3 ) is placed in the recess 30 to more uniformly spread the pressure applied on the conductor of the wire by the screw 34 . Note that the threaded engagement between the screw 34 and the contact element 14 ensures that the electrical connector 10 does not dismantle (i.e. that the body 12 does not become separated from the contact elements 14 ), for example during transportation or vibration. In a variant example, each cylindrical extension 26 includes a small, circular ledge at its top for preventing the screw 34 from projecting from, or falling out of, the topside 16 of the body 12 . From the contact element body portion 28 projects downwardly a contact portion 38 . In this example, the contact portion 38 extends the entire length of the contact element but it has a transverse dimension that is reduced relative to the transverse dimension of the contact element 14 . Note however that the contact portion 38 is not limited to any one particular shape or dimension. Rather, the contact portion 38 may assume various shapes and dimensions, a few examples of which are shown in FIG. 6 . The cages 20 receiving the contact elements 14 are dimensioned such as to allow the contact elements 14 to freely float therein, such that the contact elements 14 are movable in several different directions. Advantageously, the range of movement of the contact element 14 within the cage 20 is such as to accommodate possible co-planarity variations that may arise on the circuit board 40 or among the contact elements 14 of the electrical connector 10 . In a first direction of movement, the contact elements 14 are free to move along a vertical direction within their respective cages 20 . In the vertical direction, each contact element 14 can move in its respective cage 20 between two extreme positions. The first extreme position is shown in FIGS. 1 and 3 , where the contact portion 38 is received in the aperture 22 and projects therefrom. The second extreme position is a position in which the contact portions 38 are generally flush or slightly recessed relative to the circuit board facing side 18 , an example of which is shown in FIG. 5 . The contact elements 14 can move from one extreme position to the other in the vertical direction of movement under the effect of gravity. In the position shown in FIGS. 1, 3 and 4 , the contact elements 14 engage the bottom walls of the respective cages 20 and are held in place there. It will be appreciated that the contact element body portions 28 have transverse dimensions exceeding the transverse dimensions of the apertures 22 , such that only the contact portions 38 , which are smaller than the apertures 22 , can pass through the apertures 22 . In a second direction of movement, the contact elements 14 are also free to tilt at least in part within their respective cages 20 . This tilting movement may also be considered to be a rotation about a horizontal axis. More specifically, within each cage 20 , the respective contact element 14 is free to tilt under the effect of gravity towards or away from any one of the sidewalls of the cage 20 , such that the contact portion 38 is angled relative to the circuit board facing side 18 . Reference is made to FIG. 6 , which shows an example of the tilting of a contact element 14 within its cage 20 . The dimensions of the cage 20 determine the extreme positions between which the contact element 14 can rotate or tilt, in each of these extreme positions the contact element body portion 28 abutting against either a sidewall or the top wall of the cage 20 . In a third direction of movement, the contact elements 14 are also free to move laterally within their respective cages 20 . More specifically, each contact element 14 is free to shift within its cage 20 from side to side, between each pair of parallel sidewalls forming the cage 20 . Further, in a fourth direction of movement, the contact elements 14 are free to rotate within the cage 20 about a vertical axis. These third and fourth directions of movement will be discussed in further detail below. The electrical connector 10 is installed on a circuit board in the following manner. The electrical connector 10 is picked-up by automated equipment and deposited on the circuit board, which is typically characterized by a non-planar surface, such that the contact portions 38 of the contact elements 14 register with respective contact pads on the circuit board. Before the contact portions 38 touch the contact pads, they are extended, as shown in FIG. 1 . In other words, the contact portions 38 project from the circuit board facing side 18 . When the contact portions 38 touch the contact pads on the circuit board, the contact portions 38 start to retract under the effect of the weight of the electrical connector 10 and also under the effect of the slight pressure created by the automated equipment that handles the electrical connector 10 . The contact portions 38 continue retracting until the circuit board facing side 18 engages the circuit board surface, at which point certain contact portions 38 may have retracted more or less than others, in dependence of the non-planarity of both the circuit board surface and the electrical connector 10 . Note that during the deposition movement, once the contact portions 38 have touched the contact pads on the circuit board, the retraction of the contact portions 38 inside the electrical connector 10 is not the result of movement by the contact portions 38 themselves. Rather, the retraction of the contact portions 38 is a result of the movement of the body of the electrical connector 10 as it is deposited onto the circuit board. During deposit of the electrical connector 10 on the circuit board, the contact portions 38 of the contact elements 14 may also tilt under the effect of gravity within their cages, in order to properly engage the contact pads on the non-planar circuit board surface. Thus, the free movement of the contact elements 14 within the cages 20 serves to compensate for non-planarity of the surface of the circuit board as well as of the electrical connector itself. Further, the free movement of the contact elements 14 allows each contact element 14 to spatially self-adjust in order to maximize the surface area of the contact portion 38 that is in contact with the respective contact pad on the circuit board. An example of the position of a contact element 14 during the deposit of electrical connector 10 onto a circuit board 40 is shown in FIGS. 4 and 5 . The circuit board 40 carries on its upper surface a contact pad 42 for engagement by the contact portion 38 of the contact element 14 . The contact pad 42 is coated with solder paste. During the deposit, the contact portion 38 moves from a position that is completely extended relative to the circuit board facing side 18 to a position in which the contact portion 38 has retracted partially into the cage 20 and is tilted relative to the circuit board facing side 18 . Note that in a situation where the contact pad 42 slightly projects above the surface of the circuit board 40 , the contact portion 38 may even be slightly recessed relative to the circuit board facing side 18 , if the contact pad 42 fits within the boundary of the aperture 22 . Once the electrical connector 10 has been deposited onto the circuit board 40 , and the contact elements 14 have all self-adjusted to engage the contact pads 42 , heat is applied to solder anchor the electrical connector 10 to the circuit board 40 . The solder paste on the contact pads 42 melts and effects a permanent joint between the contact pads 42 and the respective contact elements 14 . After the installation of the electrical connector 10 on the circuit board 40 is completed, the conductors of wires are inserted in the respective contact elements 14 . The screws 34 are then tightened by inserting a screwdriver or any other suitable tool in the cylindrical bores 26 , to engage and then turn the screws 34 . During soldering of the electrical connector 10 to the circuit board 40 , as well as during use of the electrical circuit in its final application, linear changes in dimensions may arise between the circuit board 40 and the contact elements 14 , due to the expansion/contraction of the materials of the electrical connector 10 and of the materials of the circuit board 40 . This expansion/contraction of the materials occurs at different speeds and magnitudes, due to for example different CTEs, different temperature gradients or different hygroscopic properties of the materials. Advantageously, the contact elements 14 can move freely during expansion or contraction of either one of, or both, the electrical connector 10 and the circuit board 40 . More specifically, the free lateral movement, as well as the free rotational movement about a vertical axis, of the contact elements 14 within their respective cages 20 compensate for the linear changes in dimensions that may arise. This compensation through freedom of movement ensures that stresses (forces/pressures) or strains (stretching/compression) on the joints between contact elements 14 and contact pads 42 are minimized. It is not essential that the circuit board facing side 18 engage the circuit board 40 . It is possible to design the electrical connector 10 such that the contact portions 38 project from the circuit board facing side 18 and after the electrical connector 10 has been placed on the circuit board 40 the contact portions 38 retract only partially in the body 12 . In this position, the electrical connector 10 will have descended onto the circuit board 40 such that circuit board facing side 18 remains at a certain distance from the circuit board 40 . In another possible variant, the cages 20 are dimensioned such as to limit the free movement of the contact elements 14 within the cages 20 to only one or a subset of the directions of movement described above. For example, the cages 20 may be sized to allow the contact elements 14 free movement in the vertical direction only. Alternatively, the cages 20 may be sized to allow the contact elements 14 free movement in the vertical and lateral directions only, with no rotational movement possible. In yet another possible variant, the electrical connector 10 is provided with a removable gripping handle 44 as shown in the example of FIG. 7 , by which the automated equipment can more easily pick-up, transport and generally handle the electrical connector 10 during installation of the electrical connector on the circuit board 40 . The gripping handle 44 may be removed once the electrical connector 10 has been soldered to the circuit board 40 . Although various embodiments have been illustrated, this was for the purpose of describing, but not limiting, the invention. Various modifications will become apparent to those skilled in the art and are within the scope of this invention, which is defined more particularly by the attached claims.