Electrical terminal

Abstract: An electrical terminal for mounting on a circuit board, comprises a metal post having a portion (113) of increased width which has been split longitudinally to form two limbs (115,115'). The limbs (115,115') have been pushed relatively away from each other parallel to the plane of the slit to lie in adjacent parallel planes and have been subsequently pushed towards each other across the plane of the slit to bring portions (116,116') of their oppositely facing rolled surfaces adjacent to the slit, into partially overlapping face-to-face engagement, so that remote edge portions (118,118') of the limbs (115,115') are engaged with the wall of a through hole in the circuit board during insertion thereinto. The limbs (115,115') are thereby forced further together with progressive sliding engagement of the rolled surface portions (116,116') across each other further into overlapping engagement.

Description: This invention relates to an electrical terminal for mounting on a circuit board. There is described in EP-A-0257746 from which the present application has been divided, a surface mount printed circuit board connector comprising an insulating housing having a mating face and a board adjacent face, and a plurality of stamped and formed terminals with respective body portions, fixed in the housing, mating portions integrally joined to the body portions located at the mating face and an anchoring post comprising a compliant anchoring portion integrally joined to each body portion and extending from the board adjacent face wherein the connector includes a resilient contact portion trapped to extend against the surface of the printed circuit board by receipt of the compliant portion as a force fit in an unplated through-hole in the printed circuit board thereby electrically to connect a conductive path thereon to the mating portion. There is also described and claimed in said EP-A-0257746, an electrical terminal stamped and formed from a single piece of sheet metal stock and comprising a body portion adapted to be mounted in an insulating housing, from which body portion extends a mating portion and an anchoring post formed with a compliant anchoring portion adapted to be received in a through-hole in a circuit board as a force fit thereby to anchor the terminal to the circuit board, wherein a contact portion is integrally joined to the body portion by a resilient arm whereby receipt of the anchoring portion in the through-hole will urge the contact portion into electrical engagement with a conductive path on the circuit board. An example of a terminal having such a compliant anchoring portion is described in US-A-4 186 982 and comprises a post split longitudinally by shearing to form two limbs which have been pushed out in opposite directions parallel to the shear plane. When forced into a through-hole in a circuit board, the limbs are forced back together by the hole edges with progressive mutual sliding engagement of the sheared surfaces further into overlapping engagement. Terminals having compliant portions as described above have a very high retention force which is desirable when, for example, connection is to be made to the post subsequently by a wire wrapping technique. However, for this application, the very high retention force for subsequent wire wrapping is not necessary and the associated disadvantages such as a high insertion force and the problem of distortion of the through-holes together with the manufacturing difficulties arising as a result of the close tolerances to be maintained should be avoided. In addition, as a result of the requirement for sliding engagement of the sheared surfaces, the stock must be relatively thick, contributing to the problems and expense of manufacture. The present invention consists in electrical terminal comprising a metal post having a portion of increased width which is slit longitudinally to form two limbs which have been pushed out in opposite directions, relatively away from each other, parallel to the plane of the slit to lie in adjacent parallel planes, characterised in that the limbs are subsequently pushed relatively towards each other across the plane of the slit to bring portions of oppositely facing rolled surfaces thereof adjacent the slit into partially overlapping face-to-face engagement, remote edge portions of the respective limbs being engageable with the internal periphery of a through-hole of a circuit board during insertion therein to force the limbs further together with progressive sliding engagement of the rolled surface portions across each other further into overlapping engagement. The resulting insertion forces may be lower than with the prior version described in US-A-4 186 982, as the rolled surfaces have a lower coefficient of friction resisting movement of the limbs together during insertion than the sheared surfaces which are relatively rough, thereby reducing the risk of damage to through-holes. In addition, the post may be relatively thin, essentially of strip form, permitting more economic manufacture. For example, the compliant portion of the terminal may be made from stock of the same thickness (10 mil.) as that commonly used for a printed circuit board contact portion, avoiding a need for expensive premilled dual thickness stock often required with the prior version. The remote edges extend in mutually parallel relation offset in laterally opposite directions from a longitudinal medial axis of the post and are joined to an insertion end of the post by mutually divergent lead-in edge portions. For a better understanding of the present invention reference will now be made by way of example to the accompanying drawings, in which: FIGURE 1 is a cross-sectional view of a first example of a pin header aligned with as printed circuit board; FIGURE 2 is a plan view of the pin header mounted on the printed circuit board; FIGURE 3 is a cross-sectional view of the pin header mounted on the printed circuit board; FIGURE 4 is a cross-sectional view of a second example of a pin header; FIGURE 5 is a plan view of the second example mounted on the printed circuit board; FIGURE 6 is a cross-sectional view of the second example mounted on the printed circuit board; FIGURE 7 is a side elevation of a suitable low insertion force compliant portion of a terminal according to the present invention; FIGURES 8a and 8b are a front elevation and under-plan, respectively, of the compliant portion of Figure 7; and FIGURES 9a and 9b to FIGURES 11a and 11b are front elevationals and underplans showing successive stages of manufacture of the compliant portion of Figures 7, 8a and 8b. Figures 1 to 6 are included herein as being useful to facilitate an understanding of the present invention. As shown in Figures 1 to 3, the first example of pin header 11 comprises an insulating housing 12 in which are mounted a series of identical terminals 13. The housing 12 is moulded as a one-piece body of plastics material, rectangular in section and plan, and formed with a series of first and second terminal-receiving through-slots 15,15′ located in spaced-apart parallel relation along its length which communicate with opposite board-engaging and mating faces of the housing 16 and 17, respectively. Each through-slot 15 or 15′ is divided by an internal partition 18 or 18′ extending from the board mounting face part way towards the mating face 17 into first and second compartments 21 or 21′ and 22 or 22′, respectively, which intercommunicate adjacent the mating face. The first compartments 21 or 21′ are larger than the second compartments 22 or 22′, and the first and second compartments of adjacent through-slots 15 and 15′ are arranged in opposite senses, i.e. rotated through 180 degrees. As shown particularly in Figure 2, adjacent through-slots 15,15′ are also located in staggered relation with first and second slots alternating so that all first slots 15 are in mutual alignment and all second slots 15′ are in mutual alignment. As a result of the staggered disposition of the adjacent slots, a first end wall portion 23 or 23′ of each slot is less thick than a second end wall portion 24 or 24′. A clearance slot or notch 25 or 25′ opening to the board mounting face 16 is formed in each first end wall portion 23 so that opposite sides of the board engaging face 16 have a castellated appearance. Each terminal 13 is stamped and formed in one piece from sheet metal stock and includes a planar rectangular body portion 31 from respective opposite ends of which, at locations near adjacent corners, extend a post 32 formed with a compliant board anchoring portion 33, an oppositely directed mating pin 34 substantially in mutual alignment, and a board connecting portion 35 extending from one side of the body portion 31. The compliant portion 33 is of known type, for example, as described in U.S. Patent No. 4,186,982, incorporated herein, and made by splitting the post by shearing to form a pair of beam spring arms 44 pushed out in opposite directions for reception in a through-hole 36 in a printed circuit board 37 as a force fit, opposite sheared surfaces of the arms 44 being in sliding engagement during insertion. The mating pins 34 have root ends 38 bent out of the plane of the body portion 31 so that pins 34 of adjacent terminals 13 project from the mating face 17 located in precise transverse alignment over a wall between adjacent through-slots 15 or 15′ when assembled in the housing 12. The board connecting portion 35 of the terminal 13 comprises first and second cantilever elements 41,42 respectively located in substantially parallel relation by being integrally joined at first remote ends by a sinuous spring 43 comprising in effect first and second, oppositely directed, open loops or bights 45 and 46 respectively, constituted by beam elements which are rectilinear to increase their effective length. The first cantilever element 41 extends at a second end from a side or body portion 31 at a location adjacent the mating pin 34 perpendicularly away therefrom between the partition 18 and the mating face 17 across a major portion of the first compartment 21 adjacent the mating face 17 but terminating free of the end wall 23. The second cantilever element 42 extends adjacent the board engaging face with the first end adjacent the partition 18 and the free end adjacent the notch 25. The free end carries a contact foot 49 having an arcuate contact edge 51 which protrudes beyond the board engaging face 16 prior to mounting the connector 11 on the printed circuit board 37. In assembling the connector 11, the terminals are inserted one-by-one through the mating face 17 into the through-slots 15 and 15′, the compliant portions 34 passing along clearance grooves (not shown) located in opposed relation in opposite sidewalls of compartment 22. When fully assembled, the root end of the first cantilever arm 41 seats on the partition 18 and the contact foot 49 protrudes beyond the board engaging face 16 adjacent the notch 25. The connector 11 is mounted on the printed circuit board 37 by a direct plugging action, a major part of the insertion force being imposed on the edge of the body portion adjacent the mating pin, and the compliant portions 33 each received as a force fit in a suitably located through-hole 36 thereby to anchor the connector 11 on the board 37, as shown in Figure 3. Movement of the connector 11 against the board 37 causes translational movement of the foot 49 along a conductive path 43 into the notch 25 with simultaneous pivotal movement providing both a wiping action and progressively presenting a different portion of the arcuate contact edge 51 against the conductive path 43. As seen by a comparison of Figures 1 and 3, this movement is accomplished by expansion of the first loop or bight 45 and a contraction of the second loop or bight 46 with a consequential respective decrease and increase in the clearances between the first and second loops and the end wall 23 and partition 18. The connector 11 can therefore be securely anchored on a printed circuit board 37 and effectively connected thereto by a simple plugging action without recourse to plated through-holes or elaborate pre-plating techniques or soldering. The structure of the contact portion 43 provides both an advantageous soft spring constant force characteristic accommodating tolerances and the advantageous pivotal and wiping action ensuring a reliable electrical connection. In addition, the spring remains within the compartment in both flexed and unflexed conditions. The even spacing of the anchoring posts 32 assures an even stress distribution on the housing 12 during mating, with minimum distortion of the through-holes, and the staggering ensures a relatively massive supporting wall 24 or 24′ adjacent each body portion. In addition, as the contact foot and the connection point to the printed circuit board is widely spaced from the through-holes, there is also relatively little or no risk of any distortion of a through-hole upsetting a conductive path. This also enables the use of relatively wide conductive paths. The substantial axial alignment of the mating pins and anchoring posts assure that only substantially translational forces normal to the printed circuit board and the mating face are produced during mating with very little or no turning components, thereby avoiding a need for a massive housing body. A further advantage of the movement of the contact foot into the slot or notch 25 is that it facilitates access or inspection of the point of connection after mounting the connector on the printed circuit board. The second example of connector 51 shown in Figures 4 to 6 is generally similar to the first example both in structure and function except for modification in the structure of the contact portion 55 and largely consequential modifications in the housing body 56. In the contact portion 55, the first cantilever element 59 is relatively short and stiff so that the first loop or bight 57 of the sinuous spring 58 is adjacent the partition 62 and the second loop or bight 63 is adjacent an end wall 64. This enables the base of the second loop 63 to be adjacent the mating face and have an end element 65 extending for substantially the entire depth of the slot joined to a second cantilever element 69 which extends from the end wall 64 in an opposite direction to that of the first example to a location adjacent the partition 62. The second loop 63 is relatively narrow, being formed with a knee 71 at the root end. The housing 12 is modified by the provision of a slot or notch 73 in the partition 62 at the board engaging face and a further slot or notch 74 at the mating face to accommodate the knee 71. Application of the connector to the printed circuit board causes translational and pivotal movement of the foot 75 on a conductive path 76 into the slot or notch 73 again with expansion and contraction of the first and second bights respectively, as shown in Figure 6. An advantage of the second example is that less leverage is imposed on the point of connection with the printed circuit board as a result of movement of the connector during mating than in the first example as the connection point is adjacent the anchoring points. However, the conductive paths 76 must be relatively narrow in view of their close proximity to the anchoring posts and through-holes 36 past which they must extend. A lower insertion force example, according to the present invention, of terminal 111, shown in Figures 7-11b, includes a strip-form post 112 stamped and formed from sheet metal stock with a medial compliant portion 113 of greater width than an insertion end portion 114. The compliant portion 113 comprises a pair of planar limbs 115 and 115′ which extend side-by-side in parallel, adjacent planes and have mutually adjacent portions 116,116′ located in partly overlapping relation so that opposite rolled surfaces are in face-to-face engagement. Remote edges 118,118′ of the limbs 115,115′ extend in parallel relation and are joined to remote edges of the insertion end portion 114 by divergent lead-in edges 119,119′. A contact portion (not shown), having a desired function such as an edge contact for a printed circuit board, is integrally joined to the end remote from the lead-in end. As shown in Figures 9a to 9b, in one method of manufacture, the compliant portion 113 is made from a strip-form blank 121, a pair of diagonally opposite edges 122,122′ of which are then coined to provide smoothly radiussed surfaces as shown in Figures 10a and 10b. The blank is then split longitudinally by shearing along a centreline to provide a slit 123 extending completely through and beyond the medial portion 113′ and precursors 124,124′ of the limbs 115,115′ which extend in adjacent planes on each side of the slit, as shown in Figures 11a and 11b. The limb precursors 124,124′ are then pushed towards each other in parallel planes perpendicularly of the slit 123, bringing opposite surfaces of their mutually adjacent portions 116,116′ into the partially overlapping face-to-face engagement shown in Figures 7, 8a and 8b, such movement towards each other also imparting a degree of twist to the root ends 126,126′ and 127,127′ of the limbs 115,115′. It will be appreciated that, during insertion, engagement of the divergent lead-in edges 119,119′ with the plated through-hole urges the limbs 115,115′ towards each other, bringing their adjacent portions 116,116′ further into overlapping engagement with progressive sliding engagement of their rolled surfaces to establish a permanent connection to the printed circuit board. The relative proportions of plastic and elastic deformation of the compliant portion during insertion depends at least in part on the length of the slit and the width of the through-hole, but when used with typical printed circuit boards of usual practical thickness which will determine the length of the slit, the deformation will be mainly plastic.

Claims: An electrical terminal comprising a metal post having a portion (113) of increased width which is slit longitudinally to form two limbs (115,115′) which have been pushed out in opposite directions, relatively away from each other, parallel to the plane of the slit (123) to lie in adjacent parallel planes, characterised in that the limbs (115,115′) are subsequently pushed relatively towards each other across the plane of the slit (123) to bring portions (116,116′) of oppositely facing rolled surfaces thereof adjacent the slit (123) into partially overlapping face-to-face engagement, remote edge portions (118,118′) of the respective limbs (115,115′) being engageable with the internal periphery of a through-hole (36) of a circuit board (37) during insertion therein to force the limbs (115,115′) further together with progressive sliding engagement of the rolled surface portions (116,116′) across each other further into overlapping engagement.

Inventors: GILISSEN HERMANUS PETRUS JOHAN, TEURLINGS LUCAS GERARDUS CHRIS, VAN LAARHOVEN ANTONIUS PETRUS, GILISSEN, HERMANUS PETRUS JOHANNES, TEURLINGS, LUCAS GERARDUS CHRISTIANUS, VAN LAARHOVEN, ANTONIUS PETRUS
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1987
Main classification: H01R9