CONTACT PIN

Abstract: A contact pin for a printed circuit board compri­ ses a mounting portion for mounting the contact pin in a hole in the printed circuit board. The mounting portion com­ prises three legs extending the longitudinal direction of the contact pin, at least the outer legs joining a solid contact pin portion at both ends. As seen in cross section, the centre leg is bent radially outwardly and lies with its inwardly directed part between the outer legs. Both outer legs are mainly twisted to a position in which these outer legs extend obliquely outwardly from the centre leg, as seen in cross section. The centre leg is displaced radially out­ wardly with respect to the longitudinal axis of the con­ tact pin at a constant distance substantially along its whole length. As seen in cross section, the centre of the circle touching the outer side of the three legs, lies at a distan­ ce from the longitudinal axis of the contact pin in a direc­ tion radially opposite from the centre leg.

Description: The invention relates to a contact pin according to the preamble of claim 1. Such a contact pin is known from EP-A-0 105 044. In this known contact pin the outer legs and centre leg seen in cross section, extend substantially parallel to each other in an uninserted condition. When the contact pin is inserted into the hole of a printed circuit board the outer legs will move parallel with the symmetry plane of the contact pin and further a torsion of the outer legs towards each other occurs. The parallel movement of the outer legs is disadvantageous. US-A-4,066,326 discloses a contact pin of the same type, wherein both outer legs are bent radially outwardly in the opposite direction from the centre leg, wherein seen in cross section, the centre of the circle touching the outer side of each of the legs lies on the longitudinal axis of the contact pin. When the contact pin is inserted into a hole, the legs move towards each other in a direction parallel with the symmetry plane of the contact pin. Because the legs are at least partially moved back to their original position, forces extending substantially in the longitudinal direction of the contact pin are exerted on the ends of the legs, which forces result in a moment exerted on the ends of the contact pin whereby these ends are pivoted out of the original straight position. Thereby, the position of the ends of the contact pin with respect to the hole in which the contact pin is inserted, is not determined accurately anymore. When a wire wrap connection should be made with the end of the contact pin, the tool for making this connection cannot be brought in register with the corresponding end of the contact pin in the right manner anymore and this end could be bent. The same problem occurs when a connector should be mounted on the ends of an array of such contact pins. Further the pivoting movement of the ends of the pin results in a collapsing of the legs as seen in cross section, so that the contact surface between the legs and the hole is only minimal and, this contact surface is only located at the insertion side of the hole where the stresses in the printed circuit board are at a maximum. As the legs of the contact pin move mainly in the longitudinal direction through the hole, material scraped off of the lining of the wall and of the mounting portion of the contact pin, is pushed out of the hole. This material could cause a short-circuiting. US patent 4,230,384 discloses a contact pin with a mounting portion consisting of two torsion legs joining a solid contact pin portion at both ends. This known contact pin has the disadvantage that if at insertion into a relatively small hole the facing sides of the legs will contact each other no further deformation of the mounting portion for adaptation to the diameter of the small hole is possible. At small holes this could easily result in a damage of the lining of the wall of the hole. Moreover, at this known contact pin the position of the pin in the hole depends on the diameter of the respective hole. As the dimensions of the solid contact pin portions are generally standardised, the dimensions of both legs of the mounting portion of this contact pin are fixed. In practice the rigidity of the legs appears to be substantially higher than is required for providing a sufficient retaining force of the contact pin in the hole. Thereby unnecessary high stresses are caused in the printed circuit board. The invention aims to provide a contact pin of the above-mentioned kind wherein said disadvantages are obviated in a simple but nevertheless effective manner. To this end the contact pin of the invention is characterized in that both said outer legs are twisted to a position in which seen in cross section these outer legs extend obliquely outwardly from the centre leg when said contact pin is in an uninserted condition. In this manner a contact pin is obtained wherein at insertion into a hole of a printed circuit board the deformation of the mounting portion for adaptation to the diameter of the hole consists mainly of a torsion movement of both outer legs and wherein substantially no movement of one of the legs in a direction parallel with the symmetry plane of the contact pin occurs. Thereby no forces extending in the longitudinal direction of the contact pin will be exerted on the solid contact pin portions so that the ends of the contact pin will not be pivoted out of the original position. Moreover the centre leg substantially immediately provides for a positioning of the contact pin in the hole at insertion, which positioning is independent of the diameter of the hole. Further a relatively great variation of the diameter of the hole is allowable because at a relatively small diameter of the hole both outer legs may be twisted around the centre leg, while the centre leg may be pressed back between the outer legs. According to a favourable embodiment the contact point of each outer leg with the circle touching the outer side of the three legs, lies on a radius from the centre of said circle enclosing an angle with the symmetry plane of the contact pin which is more than 450. Thereby the component directed parallel to the symmetry plane of the force exerted on each of the outer legs at insertion of the contact pin into a hole, is so small that a movement of the outer legs parallel with the symmetry plane of the contact pin can hardly occur. Preferably the length of the deformed transition portion between the outer legs and the solid contact pin portions, is at least three times greater than the length of the deformed transition portion between the centre leg and the solid contact pin portions. In this manner it is obtained that at insertion of the contact pin the forces exerted on the wall of the hole increase uniformly so that a damage to the wall of the hole and the surrounding area of the printed circuit board is substantially precluded. The invention will hereinafter be further explained by reference to the drawings in which an embodiment of the contact pin of the invention is shown. Fig. 1 shows a view of an embodiment of the contact pin according to the invention. Fig. 2 is a front view of the mounting portion of the contact pin of fig. 1 on a larger scale. Fig. 3 is a side view of the mounting portion of the pin of fig. 1 on a larger scale. Fig. 4A-4E show a plurality of cross sections of the mounting portion of fig. 2 lying at different heights of the part indicated IV. Fig. 5A and 5B show two possible end positions of the legs of the mounting portion of fig. 2 after insertion of the contact pin into a hole of a printed circuit board. The contact pin 1 shown in fig. 1 comprises a mounting portion 2 for mounting the contact pin in a hole of a printed circuit board not shown in the drawings. The wall of such a hole is normally provided with a lining of copper or the like which is electrically connected with one or more conductive circuit parts of the printed circuit board. The mounting portion 2 should be designed in such a manner that at each hole diameter within the tolerance range of hole diameters on the one hand a sufficient retaining force is generated and on the other hand the lining of the hole and the surrounding area of the printed circuit board are not damaged in an unallowable manner. The mounting portion 2 of the contact pin shown in fig. 2 and 3 in more detail, comprises three legs 3, 4 and 5 extending in the longitudinal direction of the contact pin and joining a solid contact pin portion 6 at both ends. It is also possible to separate the centre leg 4 at one end from the respective solid contact pin portion 6. The solid contact pin portions have a mainly rectangular cross section wherein the corners are rounded. The mounting portion 2 is normally coated with a soldering material. The legs 3, 4 and 5 are cut out of the original solid part of the contact pin 1 such that each leg is also mainly rectangular, wherein the width of the centre leg 4 is substantially greater than the width of the outer legs 3 and 5. The width of the outer legs 3 and 5 can be chosen optimally with respect to the retaining force which is mainly determined by these legs 3 and 5. Thereby the stresses in the printed circuit board developed at insertion of the contact pin may be restricted. It is noted that the ends of the contact pin can be made in different manners depending on the application of the pin. For example, one or both ends can be designed for making a wire wrap connection or can be made as a socket. Referring especially to fig. 3 and 4A-E, both outer legs 3, 5 are mainly twisted to a position in which these outer legs extend obliquely outwardly from the centre leg 4 as seen in cross section. The centre leg 4 itself is radially outwardly displaced along substantially its whole length a constant distance with respect to the longitudinal axis 7 of the contact pin 1, so that the bent portion of the centre leg 4 is only a fraction of its total length. Fig. 4B-4E further show that the centre 8 of the circle touching the outer side of the legs 3, 4 and 5, lies at a distance from the longitudinal axis 7 of the contact pin 1 in a direction radially opposite from the centre leg. By the described construction of the mounting portion 2 of the contact pin 1 it is obtained that at insertion into a hole of a printed circuit board the deformation of the mounting portion 2 consists mainly of an inward rotation of the outer legs 3 and 5 without substantially any movement of the legs 3 and 5 parallel with the symmetry plane 9 of the contact pin 1 indicated in fig. 4E. The centre leg 4 will be elastically bent only in a small measure without any collapsing of the legs 3, 4, 5. Within the full tolerance range of hole diameters this centre leg 4 almost immediately provides for a correct positioning of the contact pin 1 in the hole. Due to the small movement of the legs 3, 4 and 5 in the direction parallel with the symmetry plane 9 of the contact pin 1 is is prevented that a force extending in the longitudinal direction of the contact pin 1 is exerted on the solid contact pin portions 6, which force would otherwise cause a pivoting movement of the ends of the contact pin 1. The centre leg 4 has a such a rounding that after insertion into a hole this centre leg has always two contact surfaces with the wall of the hole, so that all together at least four contact surfaces exist between the mounting portion 2 and the wall of the hole. This results in a steady and reliable electrical connection. The rounding of the surfaces of the legs 3, 4 and 5 contacting the wall of hole, is such that a cold weld is realised between the contact pin and the lining of the wall, which results in very favourable electrical and mechanical properties of the connection between the contact pin and the lining of the wall. Two possible end positions for the legs 3, 4 and 5 of the mounting portion 2 at a fully inserted contact pin 1, are shown in fig. 5A and 5B. Fig. 5A and 5B clearly show that the deformation of the mounting portion 2 mainly consists of a torsion of the outer legs 3 and 5, whereas the legs 3, 4 and 5 are hardly displaced. Further it appears from fig. 5A and 5B, that the contact pin 1 can be mounted in holes with different diameters, wherein on the one hand at a relatively large diameter a sufficient retaining force is exerted on the wall of the hole by the legs, whereas on the other hand at a relatively small diameter the legs can still slightly yield, so that a damaging of the wall of the hole and the adjacent area of the printed circuit board is prevented. This characteristic of the contact pin according to the invention is rather important as a damage of the wall of the hole and the adjacent area of the printed circuit board easily result in an interruption in the electrical circuits and thereby in a fault in the apparatus equiped with the contact pins. From fig. 5A it appears that at a small hole diameter the outer legs 3 and 5 are pressed against the wall of the hole at two locations so that in such cases six contact surfaces are obtained. Preferably the legs 3-5 of the mounting portion 2 are formed in such a manner that the contact point of each outer leg 3, 5 with the circle touching the outer side of the legs 3-5, lies on a radius from the centre of said circle enclosing an angle with the symmetry plane of the contact pin, which is more than 45°, preferably more than 55°. In fig. 4E a centre transverse plane is indicated by 10 and said contact points are indicated by 11 and the corresponding radius by 12. The component directed perpendicular to the centre transverse plane 10 of the force exerted on the outer legs 3, 5 at insertion into a hole and directed along the radius 12, thereby has a such a small value that a movement of the legs 3, 5 parallel with the symmetry plane 9 of the contact pin 1 can hardly occur. As appears at a comparison of fig. 2 and 3, the length along which the outer legs 3 and 5 are deformed by torsion from the solid contact pin portions 6, is at least three times greater than the length along which the centre leg is bent radially outwardly from the solid contact pin portions 6. At insertion of the contact pin 1 into a hole of a printed circuit board the forces exerted by the mounting portion 2 on the wall of the hole will thereby uniformely increase so that even at extreme circumstances no damage of the wall of the hole and the adjacent area of the printed circuit board will be caused. Fig. 4A-4E further show that the part of the centre leg 4 lying between the outer legs 3, 5 is bevelled at the sides facing the outer legs. Thereby the torsion movement of the outer legs 3, 5 towards the position shown in fig. 5A, is facilitated. In the outwardly directed side of the centre leg 4 a groove-like recess 13 is provided acting as a receiving space for any scraped off material. The invention is not restricted to the above-described embodiment which can be varied in a number of ways within the scope of the claims.

Claims: Contact pin (1) for a printed circuit board, comprising a mounting portion (2) for mounting the contact pin in a hole in the printed circuit board, said mounting portion (2) having three legs (3,4,5) extending in the longitudinal direction of the contact pin, at least the outer legs (3, 5) joining a solid contact pin portion (6) at both ends, the centre leg (4) seen in cross section in an uninserted condition being displaced radially outwardly with respect to the longitudinal axis (7) of the contact pin (1) a constant distance substantially along its whole length and lying with its inwardly directed part between the outer legs (3, 5), wherein, seen in cross section in said uninserted condition,the centre of the circle touching the outer side of the three legs (3, 4, 5), lies at a distance from the longitudinal axis (7) of the contact pin (1) in a direction radially opposite from the centre leg (4), said outer legs (3, 5) being constructed and arranged to be twisted inwardly towards each other by engagement with said hole when said contact pin (1) is inserted in said hole in said printed circuit board with said centre leg (4) remaining therebetween, said twisting of said outer legs (3,5) serving to retain said contact pin (1) in said hole, characterized in that both said outer legs (3, 5) are twisted to a position in which seen in cross section these outer legs (3, 5) extend obliquely outwardly from the centre leg (4) when said contact pin (1) is in the uninserted condition. Contact pin according to claim 1, characterized in that the contact point (11) of each outer leg (3, 5) with the circle touching the outer side of the three legs (3, 4, 5), lies on a radius (12) from the centre of said circle enclosing an angle with the symmetry plane (9) of the contact pin (1) which is more than 45°. Contact pin according to claim 1 or 2, characterized in that each end of each leg (3, 4, 5) where it joins the solid contact pin portion (6) comprises a torsionally deformed transition portion, the length of the deformed transition portions of the outer legs (3, 5) being at least three times greater than the length of the deformed transition portions of the centre leg (4). Contact pin according to anyone of the preceding claims, characterized in that the part of the centre leg (4) lying between both outer legs (3, 5) is bevelled at the sides facing the outer legs (3, 5).

Inventors: LENAERTS, JEAN PIERRE ELISABETH A., MORLION, DANNY LOUIS CORNELIUS
Applicants: BURNDY ELECTRA N.V.
Application year: 1985
Main classification: H01R9
IPC codes: H01R4, H01R12, H01R13