Patent Publication Number: US-5295862-A

Title: Connector boardlock

Description:
BACKGROUND OF THE INVENTION 
     One type of electrical connector has a housing designed to mount directly against the upper surface of a circuit board, with the connector contacts having termination ends engaged with conductive traces on the circuit board. The connector housing can be held to the circuit board by a pair of boardlocks that pass through holes in a pair of housing flanges and through corresponding holes that have been drilled into the circuit board. In most cases, the circuit board holes have been plated, with some of the plating coating the walls of the hole and additional portions lying on upper and lower faces of the board around the hole, to establish the board hole and connector housing at ground potential. With the boardlocks installed, the electrical connections between the connector and board may be soldered as by wave soldering. Each boardlock preferably has portions that abut both the upper and lower portions of the flange to lock securely to the connector during handling and shipment to the customer who will assemble it to the circuit board. Each boardlock also preferably makes firm contact with plated walls of the circuit board hole at several locations. In addition, the boardlock should offer high resistance to pullout from the circuit board in the final assembly. A boardlock which could be constructed at low cost and which provided the above features, would be of considerable value. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a low cost boardlock is provided which can be inserted through holes in a connector flange and in a circuit board to securely hold the connector and board together while assuring good electrical connection between them. The boardlock is designed to fit through a connector flange hole of a first diameter and a board hole of a second larger diameter. The boardlock is formed from a piece of sheet metal that is bent around a vertical axis to form largely tubular upper and lower hole-received portions that are received respectively in the flange hole and the larger board hole. A pair of horizontal separator slots extend from each edge of the sheet metal partially around the boardlock to allow edge regions of the lower tubular portion to be bent to a larger radius of curvature to fit tightly in the larger circuit board hole. The vertical middle portion of the boardlock, where the tubular upper and lower portions are not separated by a slot, preferably has at least one radially outward projection as in the form of a bump; the bump lies in the tubular lower portion to center it in the board hole. The tubular lower portion has slits forming a pair of fingers that extend at upward and radially outward inclines so the upper surfaces of the fingers substantially abut the lower surface of the flange. A bottom portion of the boardlock is tapered and has inclined slits that form ramps that can lie substantially under the lower board surface and which are soldered thereto, so any upward pullout force on the boardlock tends to compress solder lying between the ramp and the bottom surface of the circuit board. 
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view showing a connector installed on a circuit board by the use of boardlocks, all constructed in accordance with the present invention. 
     FIG. 2 is a front and top isometric view of one of the boardlocks of FIG. 2, ready to be installed. 
     FIG. 3 is a left side and top isometric view of the boardlock of FIG. 2. 
     FIG. 4 is a plan view of a piece of sheet metal which has been cut out, and which can be bent to form the boardlock of FIG. 2. 
     FIG. 5 is a front elevation view of the boardlock of FIG. 2, but with the top tabs not folded to the horizontal. 
     FIG. 6 is a view taken on the line 6--6 of FIG. 5. 
     FIG. 7 is a view taken on the line 7--7 of FIG. 5. 
     FIG. 8 is a view taken on the line 8--8 of FIG. 5. 
     FIG. 9 is a sectional view of the boardlock of FIG. 6, with the tabs folded, shown installed on a connector housing and circuit board, but prior to a final soldering operation. 
     FIG. 10 is a sectional side view of the arrangement of FIG. 9, but taken on a view perpendicular to that of FIG. 9. 
     FIG. 11 is an enlarged view of a portion of FIG. 9, with the boardlock fully soldered in place. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an assembly 10 of an electrical connector 12 and a circuit board 14. The connector 12 has a housing 16 that includes a pair of flange elements or flanges 20, 22 that have lower surfaces that lie facewise against the upper surface of the circuit board element or circuit board. A pair of identical boardlocks 24, 26 each extend through aligned holes 30, 32 in the connector flange and in the circuit board to mechanically and usually electrically connect them together. The connector 12 is of the type that has multiple contacts 34 with mating ends 36 that mate with the contacts of another connector, and with termination ends 38 that bear against conductive traces (not shown) on the upper surface of the circuit board and which will eventually be soldered thereto. It should be noted that terms such as &#34;upper&#34;, &#34;lower&#34;, &#34;vertical&#34;, etc. are used herein only to aid in the description of the invention, and that the parts can be used in any orientation with respect to gravity. 
     FIG. 2 illustrates details of the boardlock 24. The boardlock 24 is formed of a piece of sheet metal that was originally flat, but which has been bent to form largely tubular upper and lower hole-received portions 40, 42. The tubular upper portion 40 is designed to lie tightly within the flange hole, while the tubular lower portion 42 is designed to lie tightly within the circuit board hole. The tubular upper portion 40 has a pair of adjacent largely vertical edge portions or edges 44, 46 that are designed to bear firmly against the walls of the flange hole, while the tubular lower portion has a pair of adjacent lower edges 50, 52 that are designed to bear firmly against the walls of the circuit board hole. It is noted that it is not necessary that each edge be sharp, but can even be bent-around. The boardlock has five tabs 54 at the top which bear against the upper surface of the connector flange. The tubular lower portion 42 has a pair of fingers 56, 58 designed to substantially abut the lower surface of the flange to prevent upward pullout of the boardlock from the connector flange. The tubular lower portion also has a bump 60 along the vertical middle region or middle 62 of the boardlock, to help center the tubular lower portion in the larger circuit board hole. The boardlock has a pair of bottom tapered parts 62, 64 which facilitate insertion of the boardlock. Each bottom tapered part has slits such as 66 which form a pair of largely upwardly-facing ramps or abutments 70, 72 which can abut solder used in the final assembly. Each of these features will be discussed below. 
     FIG. 4 illustrates the piece of sheet metal 74 which has been blanked from a larger sheet, and which is to be bent into the form shown in FIG. 2. The sheet metal has a pair of separator slots 76, 78 that divide part of the tubular upper portion from the tubular lower portion. The separator slots 76, 78 leave a pair of upper edge regions 80, 82 which are separated from a pair of lower edge regions 84, 86. Each edge region extends from a boardlock vertical edge 88, 89 to the bottom 90 of a corresponding slot. The bottoms 90 of the slots are widely spaced apart, to leave a wide vertical middle 62 where the tubular upper and lower portions merge and which constitutes about one-third the width of the sheet metal. 
     FIG. 8 shows a bottom view of the boardlock of FIG. 2, showing it in relation to the holes 30, 32 in the flange and in the circuit board. It can be seen that the tubular upper portion is bent to a radius of curvature R1 so the tubular upper portion extends largely in a circle. Contact with the walls of the flange hole is made at the corners 100, 102 and at the vertical middle 62. The tubular lower portion 42 has a middle which is substantially a vertical extension of the middle of the tubular upper portion. However, the lower edge regions 84, 86 are bent so part of each extends substantially straight to leave corners 104, 106 that engage the walls of the circuit board hole 32. The average radius of curvature of a lower edge region such as 86 is much larger than the average radius of curvature of the upper portion 40. The radius of curvature of the region 86 can be considered to be the radius of curvature of an imaginary circle that lies on point 110 at the bottom of the separation slot, on a point at 104 formed by the edge, and on a point 112 that is halfway in between the other two points. The bump 60 serves to provide three points of contact (at bump 60 and edges 104, 106) to position the tubular lower portion 42 in the circuit board hole, so the boardlock tends to remain untilted, that is, so its axis tends to remain vertical and coincident with the axis of the flange and board holes. Without the bump 60, the lower part of the vertical middle would tend to be pressed towards the walls of the hole. 
     FIG. 10 shows the boardlock 24 installed in the holes 30, 32 of the connector flange 20 and of the circuit board 14. The flange has upper and lower surfaces 120, 122, while the circuit board has upper and lower surfaces 124, 126. The boardlock is initially installed in the flange 20 and the connector is shipped with the boardlock in place, to the customer. The customer has holes drilled in his circuit board, and presses the connector with the boardlocks thereon, downwardly so the boardlocks enter the holes in the circuit board. The two fingers 56, 58 are each formed by a pair of slits 130 (FIG. 4) on the lower side of each separation slot 76, 78. As shown in FIG. 10, each finger is bent so its upper end 132 lies further from the axis 134 of the boardlock than the lower end of the finger. The upper end of each finger lies at the upper end of the circuit board hole, and lies substantially abutting the lower face 122 of the flange. Thus, once the boardlock has been pressed downwardly through the flange and circuit board, the boardlock is locked in place against upward pullout of the flange. The fact that the hole 32 in the circuit board is larger (preferably at least 5 percent larger) than the hole in the flange, results in providing room at the bottom surface 122 of the flange beyond its hole 30, against which the finger upper ends 132 can press. 
     As shown in FIG. 4, slits 66-69 are formed at opposite sides of each bottom tapered part 62, 64. As shown in FIG. 2, the portion under each slit such as 66 forms a bottom tab 140 which is bent further from the axis 134 than the lower edge region such as 86 lying above the slit 66. This results in the upwardly-facing ramp or abutment 70, 72. Referring to FIG. 11, the upwardly-facing abutment 72 is bent sufficiently that it lies either directly below the bottom surface 126 of the circuit board 14 at its point of intersection 144 with the hole 32, or lies very close thereto. After the connector with boardlocks has been installed, the circuit board may be subjected to wave soldering, which results in filling the gap 146 between the tubular lower portion 42 and the walls of the circuit board hole 32 with solder. One trapped solder portion 150 lies between the abutment 72 and the corner 144, by lying either directly below it or close to a position directly below it. When an upward force is applied to the boardlock 24, the trapped portion 150 is subjected to compression force between the abutment 72 and the board lower surface 126. Tin lead solder is weak in shear, but is stronger in compression. The fact that an appreciable quantity of the solder is under compression force when the boardlock is pulled upwardly relative to the circuit board, results in the solder being able to withstand significantly greater pullout forces than it could in the absence of such compression loading of the solder. Applicant prefers to angle the ramp or abutment 72 at an appreciable angle A from the horizontal, the angle shown being about 22° and preferably being at least about 15°. Such angling assures that part of the abutment 72 lies closely below the lower surface of a circuit board for boards of a range of thicknesses such as between about 54 and 70 thousandths inch. 
     Applicant has designed a boardlock of the construction shown, with an overall height between the bottom and the bent-over tabs 54 of 0.185 inch (4.70 mm). The boardlock was designed to fit into a circuit board hole having a diameter of 0.109 (2.77 mm) and a flange hole of a diameter of 0.089 inch (2.26 mm). The relative shape of the parts of the boardlock are as shown in the figures. 
     Thus, the invention provides a connector which mounts facewise against a circuit board, with boardlocks of low cost that reliably mechanically and electrically connect the connector housing to the circuit board. The boardlock is formed from a piece of sheet metal that has opposite vertical edges and a vertical middle, the boardlock having at least one separation slot separating it into tubular upper and lower portions, with the separation slots preferably extending largely horizontally from each vertical edge. The tubular lower portion has edge regions below each separation slot, that are bent to a larger average radius of curvature than edge regions of the tubular upper portion lying above the slot. This allows the tubular lower portion to lie snugly within a larger diameter hole in the circuit board. The lower tubular portion has a projection in its vertical middle portion or middle, such as in the form of a bump, to center the tubular lower portion in the circuit board hole. The tubular lower portion has a pair of fingers that are bent to extend upwardly and radially outwardly with respect to the axis of the boardlock, so upper ends of the fingers which lie within the larger circuit board hole, can abut the lower surface of the housing flange. The boardlock has tapered bottom portions with slits forming abutments that lie closely below the lower surface of the circuit board, to provide compression resistance of solder therebetween to resist upward pullout of the boardlock from the circuit board. 
     Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.