Holdown Key for Low Profile Connector

Electrical connectors that mount on the surface of a circuit board, can each include a connector housing that lies on the circuit board, multiple contacts with tails that press against corresponding pads on the surface of the circuit board, and a pair of keys at opposite ends of the connector housing that project through holes in the circuit board to retain the connector housing to the board. The keys may include a pair of largely vertical legs that are pressed down into the circuit board holes and that have barbs that dig into the walls of the holes. As the legs are pressed into the hole, the legs are resiliently deflected toward each other to provide a large holding force at the barbs. The keys hold the connector in place prior to soldering, and serve to relieve pressure on the solder joints that join the contact tails and circuit board pads when the connector is unmated from another connector and forces are applied that tend to pull the connector off of the board.

At present, a "standard" and widely used holdown key is formed of sheet metal and has a pair of legs whose upper ends merge and whose lower ends are free to deflect together. U.S. Pat. No. 5,080,611 describes keys of this type. Such legs can apply only a moderate resistance to deflection, and therefore can apply only a moderate retention force. Keys have been proposed wherein both the upper and lower ends of the legs merge, resulting in high resistance to bending of the beams toward each other. U.S. Pat. No. 4,907,987 describes keys of this type. Although merging the upper and lower ends of the keys makes the legs highly resistant to deflection toward each other, they can deflect only a moderate distance before plastic deformation begins. As a result, if there is poor matching of the key and circuit board hole, as where the hole is of maximum diameter and the distance between the key legs is minimum, this may result in only a very small or nonexistent retention force. Also, such keys can be difficult to stably mount in the connector so they remain stably in position prior to installation on a circuit board. A connector with holdown keys which could apply large retention forces in the most common cases, but which still applied moderate holdown force under "worst" case conditions, and which facilitated retention on the connector prior to mounting of the connector on a circuit board, would be of considerable value.

In accordance with one embodiment of the present invention, an electrical connector is provided which has a pair of keys for insertion in holes of a circuit board, wherein each key can provide high retention force in the circuit board under normal conditions, which reduces the possibility of plastic deformation under conditions of high interference fit, and which provides moderate retention force under conditions of low interference fit, and wherein the key is easily securely installed in the housing of the connector. Each key lies in a slot at the end of the connector housing and has a pair of largely vertically extending legs, with the legs extending below the bottom of the connector to enter a circuit board hole which deflects the legs toward each other. First ends of the legs merge and the opposite ends of the leg are free of each other but have locations that abut each other when the legs are deflected toward each other. The abutting locations are close enough that the legs can be deflected together until the locations abut each other, without substantial plastic deformation of any portion of the key. The presence of free ends allows the legs to be resiliently deflected by a large amount, which can assure at least moderate retention force in a large board hole and which can aid in retention of the key in the connector housing before the connector is installed on the circuit board. The fact that the free ends abut each other when the key is fully installed in the circuit board, results in large resistance to further deflection of the legs toward each other, to provide for high retention force under most circumstances.

The upper end portions of the legs can form upper projections while the middles of the legs can form lower projections. The projections form shoulders that abut upper and lower key-support surfaces on the connector housing to fix the position of the key on the connector housing prior to installation of the connector on the circuit board. The key is preferably formed with the upper ends of the legs being free and the lower ends of the legs merging, with barbs that engage the walls of the circuit board hole lying closer to the lower ends of the legs than to the upper ends thereof.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

FIG. 1 is a partially sectional isometric view of a connector system which includes a pair of connectors that are each mounted on a corresponding circuit board, with the connectors lying close to a position where they would begin to mate.

FIG. 2 is a plan view of a socket, or female connector of the system of FIG. 1.

FIG. 3 is a partially sectional side view of the connector of FIG. 2.

FIG. 4 is a side view of the holdown key of the connector of FIG. 3, shown in its initial, undeflected configuration.

FIG. 5 is a side view of the key of FIG. 4, showing it installed on the connector housing and in the circuit board, so the key is in its fully installed and deflected position, the figure also showing, in phantom lines, the key in a partially deflected position.

FIG. 6 is a side elevation view of a holdown key constructed in accordance with another embodiment of the invention.

FIG. 1 illustrates a connector system 10 which includes a pair of connectors 12, 14 that can mate, with each connector mounted on a corresponding circuit board 16, 18. The connector 14 has multiple pin contacts 20 that each has a tail 22 that presses against a conductive pad 24 on the circuit board 18 when the connector lies on the circuit board. Similarly, the connector 12 has a plurality of socket contacts 26 with tails 28 that engage conductive pads on the circuit board 16. Each connector such as connector 12 includes an insulative connector housing 30 that holds multiple contacts, and which has opposite ends 32, 34 that are held to the corresponding circuit board 16 by a pair of keys 40, 42. Each key projects through a corresponding hole 44, 46 formed in the circuit board 16. It may be noted that the diameters of the circuit board holes such as 44, 46 and their spacing, as well as the size and spacing of the pads on the surface of the circuit board, have been set by current standards, and a connector generally should be constructed so its parts can fit a circuit board constructed to those standards in order to gain wide acceptance in the industry.

FIGS. 2 and 3 illustrate some details of the socket or female connector 12. Each end 32, 34 of the connector housing 30 has a vertically-extending slot 50 which receives a key 40, 42. As shown in FIG. 3, the key has an upper portion 52 which lies in an upper portion 54 of the slot, and has a lower portion 56 which lies in and below a corresponding hole 44 in the circuit board 16. The key has a pair of legs 60, 62 which have barbs 64, 66 at their lower ends for "biting" into the walls of the circuit board hole 44 to retain the key, and therefore the entire connector 12, to the circuit board. The legs 60, 62 are deflected together when the lower portion 56 of the key is inserted into the circuit board, to firmly anchor the barbs 64, 66 in the circuit board. It can be seen from FIG. 2, that the particular key 50 is planar and is formed of a sheet of metal, so that it has a substantially uniform thickness, and can fit closely in the slot 50 of the connector housing.

FIG. 4 illustrates details of the key 40, showing it in its initial configuration, before it is installed on the connector housing. The key is symmetrical about a vertical axis 68, so the legs 60, 62 are mirror images of each other. Each leg has an upper end portion 70, 70a, a lower end portion 72, 72a, and a middle 74, 74a. The lower end portions 72, 72a merge at 76, and the arms cannot move or pivot relative to each other at the joined or merged location 76. The upper end portions 70, 70a of the arms are free of each other, so they can move towards and away from each other. Each upper end portion has a protuberance forming a convex abutting location 80, 80a. The abutting locations can abut each other when the upper end portions of the legs are deflected together. The legs are long and thin enough, and the abutting locations 80, 80a are close enough, that the locations can abut without plastic deformation of any portion of the key (relative to the shape of the key in its initial configuration of FIG. 4). When the convex locations 80, 80a abut each other, the upper end portions 70, 70a of the arms can still pivot relative to each other, as opposed to being fixed to each other as are the lower end portions. FIG. 4 shows the initial control gap at A, the partially closed gap at B which exists when the key is installed on the connector but not on the circuit board, and also shows the fully installed gap C which has zero width and which occurs when the key is fully installed in the circuit board.

FIG. 5 shows the key 40 after it has been installed on the connector housing 30, and after the connector housing with the key thereon has been installed on the circuit board 16, but prior to soldering of the circuit board. It can be seen that the gap C is fully closed, and the barbs 64, 64a and 66, 66a press firmly against the walls 82 of the circuit board hole 40. The circuit board includes a base 84, and may also include a layer 86 of conductive material on the walls of the hole (or may not include such layer). The arms have been deflected together sufficiently for the barbs to dig into the walls 82 of the hole to securely anchor the key in place. Usually, after such anchoring the assembly is soldered to solder the metal key to the plated walls of the hole. Whether soldered or not, the dug-in barbs securely anchor the connector housing in place to resist upperward forces in the direction U which occur when a mating connector is unmated from the connector 12. Very secure anchoring of the barbs in the board holes is required even in the case of soldering, to avoid large forces on the solder which cannot be withstood by it.

The connector 12 can be initially assembled by installing the key 40 into the connector housing slot 50, with installation in the circuit board holes occurring later. It is highly desirable that the key be securely retained in the slot 50, and in a manner that closely fixes the orientation of the key in the slot, to assure that the tapered nose 90 at the bottom of the key will later accurately enter the circuit board hole. Each leg 60, 62 of the key includes upper projections 92, 92a and lower projections 94, 94a which serve to retain the key on the connector. When the key is installed in the connector slot, a downwardly-facing upper shoulder 100 on the upper projection 92 lies substantially against an upper key-supporting surface 102 on the connector housing. Also, at that time a lower shoulder 104 on the lower projection lies adjacent to a lower key-supporting surface 106 on the connector housing. The upper and lower shoulders 100, 104 prevent the key from moving substantially up and down relative to the connector housing.

When the key is installed, it lies in the position 40A shown in phantom lines in FIG. 5, with the arms 60, 62 having been deflected together so the gap has the partially closed width shown at B. This is caused by in the outer surfaces 101, 101a of the arms that lie between the shoulders 102, 104 bearing against the walls of a narrowed slot portion 110 which lies between the upper and lower surfaces 102, 106. The pressure of the legs against the narrow slot portion 110 results in the key being held stably in position and with the nose 90 lying substantially on the vertical axis 112 of the slot. Such firm holding of the key not only helps assure alignment of the key with the circuit board hole, but also prevents "rattling" of the key on the connector, which detracts from the appearance of quality of the connector as where the connector with the key installed therein is sold to a customer who will install it on a circuit board.

During installation of the key projections 94, 94a in the connector, the legs 60, 62 must be pressed tightly together until the abutting locations such as 80 abut each other and the control gap width C is zero. Also, the beams are bowed inwardly towards each other to allow the projections 94, 94a to pass through the narrow slot portion 110. There is only moderate stress on the material of the key during such inward bowing of the beams, because of the fact that the abutting locations 80, 80a, can pivot relative to each other, as opposed to being rigidly fixed to each other as are the lower ends of the legs. It is noted that the barbs 66, 64 lie much closer to the lower end of the beams (at the merged location 76) than to the upper ends at the abutting locations, which has the advantage of providing considerable resistance to deflecting the barbs toward each other so they are anchored securely in the circuit board hole. It is noted that during installation on the circuit board, tools are applied to the upper surface 112 of the connector ends and the top surfaces 114 of the keys to press down the keys into the circuit board holes.

Applicant has constructed connectors of the type illustrated in FIGS. 1-5 and found them to operate well. Each key had an overall height A (FIG. 4) of 0.187 inch (4.75 millimeters). The height A also can be expressed as 187 mils (one mil equals one thousandth inch). In the initial configuration shown in FIG. 4, the separation B of the outside 101, 101a of the legs between the upper and lower shoulders 100, 104 was 43 mils (1.09 mm) .+-.2 mils (.+-.0.05 mm), the distance C between the lower projections 94, 94a was 58 mils (1.47 mm) .+-.2 mils, the distance D between the upper barbs 66, 66a was 55 mils (1.41 mm) .+-.2 mils, and the distance E between the lower barbs 64, 64a was 54 mils (1.38 mm) .+-.2 mils. The width of the initial control gap A was 10 mils (0.25 mm) .+-.1 mil (0.03 mm). As indicated in FIG. 5, the inside diameter F of the circuit board hole was 47 mils (1.19 mm) +2 mils (+0.05 mm) or -3 mils (-0.08 mm). The key was formed of plated phosphor bronze sheet metal having a thickness of 8 mils (0.2 mm), and the slot in the connector housing which receives the key had a width of about 10 mils (0.25 mm). It should be noted that in the present descriptions, terms such as "upper", "lower", "vertical", etc. have been used to aid in the description of the invention, but it should be understood that the parts can be used in any orientation with respect to gravity.

FIG. 6 shows another key 120 which can be installed in the housing slot of FIG. 5. The key 120 has a pair of arms 122, 122a with lower end portions 124, 124a designed to project through a circuit board hole and to hold a pair of barbs 130, 132 in the circuit board hole. However, the lower end portions 124, 124a are unconnected so they are free to deflect toward and away from each other. Opposite upper end portions 134, 134a of the arms are rigidly connected together, with the upper end portions being designed to lie in the slot of the connector housing. When the key is pushed down into the hole of a circuit board indicated at 136, a pair of abutting locations 140, 140a are deflected together, so that further movement of the barbs such as 130a towards each other results in inward bowing of the beams towards each other. The abutment of the abutting locations 140, 140a results in moderately high resistance of the beams and barbs thereon to deflection towards each other, and yet stresses in the lower end portions 124, 124a of the beams is minimized because the beams are not rigidly connected to each other but can pivot relative to each other about the abutting locations 140, 140a.

Thus, the invention provides an electrical connector with keys that project into holes of a circuit board when the connector is mounted on the board. Each key has a pair of largely vertically extending arms that are deflected closer together when the lower portion of the key is projected into the circuit board hole. Applicant constructs the key so that first adjacent ends of the legs are rigidly joined together by merging into each other, while the opposite second end portions of the legs are free to move towards and away from each other but have abutting locations that abut each other when the arms are installed fully into the circuit board hole. The key lies in a narrow slot in the connector housing, and the slot can have a narrow portion which holds part of the middle of the key. The key has upper and lower shoulders that abut corresponding surfaces in the slot to prevent upward or downward movement of the key relative to the connector housing. The merged ends of the legs are preferably at the lower ends of the legs which project into the circuit board hole, so the merged lower ends can form a fully tapered nose to accurately enter into the circuit board hole.