Circuit Board and Edge-Mountable Connector Therefor, and Method of Preparing a Circuit Board Edge

The present invention relates to a circuit board and an electrical connector mountable to an edge thereof and more particularly to means for interconnecting ground circuitry on the circuit board with ground posts on the connector.

In certain high density circuit board applications such as board to board interconnections one of the mating connectors is attached to the edge of one of the boards and the other connector is either attached to the edge or the surface of the other board. Such connectors, when mounted to the edge of the board, occupy less board space than their surface mount counterparts, and therefore are more desirable in these applications. Examples of these types of connectors are disclosed in U.S. Pat. Nos. 5,199,885 and 5,127,839 which issued to Korsunsky et al. on Apr. 6, 1993 and Jul. 7, 1992 respectively. In such edge mounted connectors, the signal contacts generally have solder tails that extend outwardly in two parallel rows, one row of tails being in contact with pads on one side of the circuit board and the tails in the other row being in contact with pads on the opposite sides of the circuit board. The ground contacts are positioned so that their posts extend outwardly in a row between and parallel with the two rows of signal contact solder tails. The ground posts extend into holes in the edge of the circuit board and engage transversely arranged plated through holes that are interconnected with ground circuitry on the circuit board. Solder paste in the plated through holes and on the contact pads is reflowed, to effect soldered connections between the posts and solder tails and their respective holes and pads.

As the circuitry on these circuit boards becomes more dense the edge mounted connector must become correspondingly smaller resulting in very delicate contacts. Any variation in alignment during assembly of the connector to the circuit board may cause the contacts to become imaged. Therefore, precise alignment is necessary. This requires that the holes in the edge of the circuit board be very precisely located between the two major surfaces. It is known to drill or to pierce or punch these holes from the edge of the board inwardly toward and through the wall of the plated through hole. This tends to cause portions of the insulating circuit board to enter the plated through hole and to interfere with the subsequent soldering process, and such debris must be cleaned out prior to soldering. Additionally, these holes are only about 0.018 inch square making the punch tooling fragile and easily damaged. As a result, these openings are difficult and extensive to make properly accurately located and dimensioned. What is needed is a way of interconnecting the posts to the edge-mounted connector with the plated through holes of the circuit board without the need of forming holes into the edge of the board.

A circuit board is arranged to receive an electrical connector mounted to an edge thereof. The present invention comprises defining openings along the edge which extend from the edge surface inwardly to intersect the plated through holes, and which extend from one major surface toward the other major surface or which are slots extending completely to the other major surface. Posts of a connector are insertable through the openings and are electrically connected to the plated through hole spaced inwardly from the edge surface. The connector posts may be ground posts of bus bars, or may be posts of signal contacts or power contacts of the connector or even posts of a shield member surrounding the connector. The connector may have one such post in addition to other contacts of conventional design, with the one post insertable into one slot in the board edge, such as for shielding or power.

In one specific embodiment, the connector includes signal contacts having solder tails adapted to be interconnected to circuitry on the circuit board and ground contacts having posts adapted to be interconnected to ground circuitry on the circuit board. The circuit board has all edge and two opposite major surfaces extending from the edge, electrically conductive contact pads on at least one of the surfaces in electrical engagement with circuitry on the circuit board, and a plurality of plated through holes adjacent the edge, substantially perpendicular to the major surfaces and in electrical engagement with ground circuitry on the circuit board. A plurality of slots are formed in the edge of the circuit board extending from one of the two major surfaces toward or to the other major surface, wherein each slot intersects a respective one of the holes. Each of the slots is adapted to receive a respective one of the posts so that the axes of the posts are generally parallel with and between the two major surfaces and in electrical engagement with respective plated through holes, such as through soldering. Alternatively, the posts may extend into the respective slots angled slightly upwardly and downwardly alternating along the row of solder tails, thus when soldered, altogether defining an improved mechanical retention to the board edge. Also the posts may have ends which are all angled slightly in one direction.

In another embodiment a conductive insert is secured within each plated through hole and which includes portions gripping a post inserted through the slot and into the plated through hole, while a pair of spring arms establishes an electrical connection therewith. Afterward soldering of the post to the insert may be performed to complete the electrical and mechanical connection.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings.

FIG. 1 is an isometric view of a portion of a circuit board and connector assembly incorporating the teachings of the present invention;

FIGS. 2 and 3 are plan and cross-sectional views of one of the plate through holes shown in FIG. 1, with FIG. 3 being taken along lines 3--3 of FIG. 2;

FIG. 4 is an enlarged isometric view of a plated through hole and an opening extending from the edge to the through hole and partially from one major surface toward the other;

FIG. 5 is a cross-sectional view similar to FIG. 3 in which alternating ground solder tails are angled upwardly and downwardly in the slots and through holes;

FIG. 6 is an isometric view of a portion of the circuit board shown in FIG. 1, positioned in a tool for shearing the slots in accordance with the present invention;

FIGS. 7 and 8 are plan and cross-sectional views of one of the plated through holes shown in FIG. 1 having an insert therein, with FIG. 8 being taken along lines 8--8 in FIG. 7 prior to insertion of the post;

FIG. 9 is a view similar to that of FIG. 8 showing the post fully inserted; and

FIG. 10 is a flat pattern view of the insert shown in FIG. 7 after stamping but with the carrier strips attached.

There is shown in FIG. 1 a portion of an edge mounted electrical connector 10 and a circuit board 12 to which the connector is attached. The circuit board 12 has two opposite substantially parallel major surfaces 14 and 16 which extend from an edge 18. Metalized circuitry 20 is arranged on each of the major surfaces and terminates in any one of several contact pads 22 that are arranged on the two surfaces, or any one of several plated through holes 24. The plated through holes 24, in this example, are connected to ground circuitry on the circuit board with centers thereof spaced inwardly from the edge surface a distance greater than the radius of the holes so that dielectric material of the circuit board remains between the plated through holes and the edge surface. A plurality of board openings such as holes 26 are formed in the edge 18 so that one slot is in alignment with and intersecting each respective plated through hole 24, and having dimensions less wide than the diameters of the holes. The connector 10 includes a housing 28 having a ground bus 30 extending along its longitudinal center with posts 32 projecting from the housing, through respective slots 26, and into respective plated through holes 24, with axes thereof generally perpendicular to the edge surface and generally parallel to the major surfaces. FIGS. 2 and 3 show, in more detail, one of the posts 32 fully inserted into a plated through hole 24 at least extending thereinto, with the tip 50 shown almost touching the far wall of the plated through hole. A row of upper contacts 34 and a row of lower contacts 36 project outwardly from the housing 28 on either side of the ground bus 30 and have solder tails 38 and 40 respectively in contact with their respective contact pads 22, as shown in FIG. 1.

In another embodiment of the present invention shown in FIG. 4, an opening 27 is shown provided along card edge 18 extending only partially through board 12, extending from major surface 14 to just beyond medial plane 44, and intersecting the side of through hole 24. Side walls of opening 27 may be chamfered.

FIG. 5 illustrates that the posts 32a, 32b may be angled slightly upwardly and downwardly as they extend through slots 26 and into through holes 24 where they are soldered; the angles may be for example about 15.degree.. The alternatingly angled posts are seen to provide a more effective mechanical joint upon soldering. The posts may also be all angled slightly in a common direction.

The slots 26 are made by means of a shearing tool 60 as shown in FIG. 6. The shearing tool includes a shear blade 62 having a straight back edge 64 that is substantially parallel with the axis of the plated through hole 24 and a front edge 66 that tapers away from the back edge so that the two edges diverge away from the tip 68. The tip 68 is smaller than the inside diameter of the plated through hole 24 and is inserted therein prior to the front shearing edge 66 engaging the wall of the plated hole so that shearing occurs from the inside out. A downwardly facing surface 70 of the shear blade 62 forms a push surface for pushing the sheared slug (not shown) away from the circuit board. A shear block 76 is attached to a base plate 74 by means of screws, not shown. The shear block 76 has a plurality of die openings 78 in alignment with the plated through holes 24, each of which is dimensioned to closely receive a respective shear blade 62 as it is forced downwardly into the associated plated through hole, from its position shown in FIG. 6. As the shear blade 62 moves downwardly, it severs a section of the circuit board and hole plating, pushing it into the die opening 78. As the shear blade 62 continues to move downwardly, the sheared slug is pushed into a clearance opening (not shown) in the base plate 74 beneath die opening 78 where it is discarded. This produces a relatively clean slot with no debris or contamination within the plated through hole. The openings formed by the plated through holes 24 are filled with a suitable solder paste 84, as shown in FIGS. 2, 3 and 5. Additionally, solder paste, not shown, is applied to the contact pads 22 which are to be soldered to the solder tails 38 and 40.

The opposing contacts 38 and 40 are spaced slightly closer together than the thickness of the board but with a lead-in 42 so that when the connector is moved toward the board and into engagement therewith, the lead-in portions of the contacts engage the edges of the board and cam outwardly then slide along the surfaces of the board until they engage their respective contact pads 22. Additionally, as the connector is being moved toward the edge of the board, the posts 32 enter their respective openings 26 and enter and engage the plated through holes 24, displacing a slight amount of solder paste 84 (FIGS. 2, 3 and 5). The slots 26 have a width that is a slight interference fit with the posts 32 so that the friction between the slots and the individual posts firmly holds the connector 10 in place until the soldering operation can be completed. After assembly the unit is then subjected to a heating operation to reflow the solder paste so that each of the posts 32 and solder tails 38, 40 are soldered to their respective plated through holes 24 or solder pads 22.

Preferably, the amount of solder paste injected into through holes 24 is controlled such that the solder paste is recessed below the major surfaces 14,16 so that when the connector 10 is assembled to the circuit board, as set forth above, those solder tails 38 and 40 which pass over the plated through holes 24 will not pick up small amounts of the solder paste contained therein which could otherwise create a trail or bridge of solder paste between two adjacent pads 22 leading to short circuits.

In another embodiment of the present invention, there is shown in FIGS. 7 and 8 one of the plated through holes 24 with an insert 90 in place as an alternative to using solder paste. The insert 90 includes a cylindrically shaped portion 92 having an outside diameter that is a slight interference fit with the inside diameter of the plated through hole 24. The amount of interference is lust sufficient to retain the insert within the hole until after the connector 10 is assembled to the circuit board 12. The cylindrically shaped portion 92 has an elongated opening 94 that is parallel with the axis of the cylinder. The elongated opening 94 is defined by two relatively straight sides 96 and 98 that are turned inwardly and spaced apart a distance that is less than the thickness of a post 32. A pair of opposing Spring members 100 and 102 extend from opposite ends 104 and 106 respectively of the insert 90 diametrically opposite the elongated opening 94. The spring fingers are bent toward each other and toward the elongated opening 94, then each is curved outwardly through the opening 94 and into the slot 26, as shown in FIG. 8. This assures that the elongated opening 94 is in alignment with the slot 26 when the insert 90 is inserted into the plated through hole 24. The two spring fingers 100 and 102 form opposing convex surfaces 108 and 110 respectively which define a constriction and which diverge toward the elongated opening 94 concluding in free ends 112 and 114 respectively which form a lead-in for insertion of the post 32. The convex surfaces 108 and 110 are spaced apart a distance that is less than the thickness of the post 32. A mound 116 of solder is deposited on the inner surface of each spring finger adjacent the convex surfaces 108 and 110 as shown in FIG. 8.

As the post 32 is moved into the slot 26, it wedges between the two convex surfaces 108 and 110 causing them to spread apart slightly. As movement continues the tapered end of the post enters between the edges 96 and 98 causing them to spread apart thereby locking the cylindrical portion 92 against the interior of the plated through hole 24. The two edges 96 and 98 tend to dig into the surfaces of the post slightly thereby gripping it and holding it securely in the slot 26. This effectively holds the entire connector 10 to the circuit board 12 until the soldering operation is complete. When the poet 32 is fully inserted into the slot 26 its tip 50 is preferably at least close to the back inside surface of the cylindrical portion 92, as shown in FIG. 9.

The insert 90 is shown in flat pattern form in FIG. 10. The mounds 116 of solder may be deposited by any thick film printing technique that is well known in the industry. Flux may be added to the solder mounds prior to the solder reflow process. The cylindrically shaped portion 92 is roller from rectangular portion 92' into its cylindrical shape by suitable tooling, not shown, and the edges formed inwardly to define the elongated opening 94. Note that the insert is attached to two carrier strips 118 which are severed prior to forming the spring fingers 100 and 102 into their arcuate shapes and insertion of the completed insert 90 into the plated through holes 24.

An important advantage of the present invention is economically providing accurately positioned openings in the edge of the circuit board extending to the plated through holes spaced from the edge surface, without having to drill or punch holes into the edge surface or risk debris remaining in such holes, thus reducing the cost to manufacture the product and increasing its reliability.

Variations and modifications may be devised to the embodiments disclosed herein, which are within the spirit of the invention and the scope of the claims.