US 3470522 A
Description (OCR text may contain errors)
I Sept. 30, 1969 I R. LAWRENCE 3,470,522
ELECTRICAL CONNECTOR Original Filed Aug. 12, 1965 a I VENTOR I Passer [A weaves AGENT U.S. Cl. 339-14 7 Claims ABSTRACT OF THE DISCLOSURE A strip type multi-contact connector for communicating with a plurality of spaced apart conductor pads or terminals carried on a circuit board. Each contact is comprised of a specially cut and shaped round spring wire forming a pair of individual contact units extending generally in parallel relationship to one another, but each being of a different length. Each contact unit comprises a substantially arcuate shaped beam portion cantilevered from a first end of a resilient arm and carrying a terminal engaging portion. The second ends of the arms are integrally joined to form a loop adapted to serve as a connection point.
This application is a continuation of my application Ser. No. 479,182, filed Aug. 12, 1965, now abandoned.
This invention relates to electrical connectors and more particularly to a pressure strip connector having a plurality of flexible contact members for communicating with a plurality of spaced apart connection pads or terminations carried on a circuit board.
One type of conventional electrical connector is generally referred to as being of a pin and socket type wherein a plurality of straight connector pins are forcibly mated by means of an interference fit into a plurality of receptacles or sockets so that mechanical and electrical contact takes place between the mated parts. The insertion and withdrawal forces necessary to overcome the frictional contact inherent in the joining of a pin and socket type connector is normally quite high. Individual pin alignment with a mating socket poses a problem in that the pins often become bent or broken which causes misalignment that results in faulty contact between the connector elements.
It is a general requirement with any such electrical contact that for reliability of continuous connection, there be a positive force holding the contact member and the conductive area or terminal in contact. The greater the contact pressure the greater the reliability ranging from a contact pair which intermittently opens, due, for example, to vibration or to differential thermal expansion, to a contact pair with such pressure that damage is caused to the contact surfaces. Therefore, in general, contact pressure must be compromised to provide insertion ease and to prevent damage or inelastic springing of the contacts.
A further disadvantage of prior art electrical connector devices resides in the fact that dimensional tolerances are exceedingly small so that long term shrinkage of the basic material (such as plastic) of which the male and female elements of the connector are made produces misalignment of the contact members which in turn result in unreliable electrical connection.
One typical prior art attempt to solve this critical dimensional stability problem has been to provide independently mounted contacts which are fingerlike, interleaved, and split whereby each member slides between the separated portions of the other. This system, however, requires very small tolerances in the placement and alignment of the contact to preclude damage from any false United States Patent or misaligned insertion. In addition, this approach requires an expensive, additional nonprintable step in the manufacture of the circuit board and is also subject to the compromise discussed above regarding contact pressure.
A further problem involved in the utilization of modular printed circuit boards is that of providing a means for locking the board securely in place such that the locking means does not detract from the advantages such as compactness, high density arrangement of contacts and accessibility otherwise incumbent or available with removable modular circuit boards. Prior art systems have typically required elaborate locking bars over entire sets of inserted panel boards because it would require excessive space and Weight to provide a locking bar for each board. However, such an overall locking bar is in itself, bulky so that when the bar is removed to permit withdrawal of one panel, many other panels are affected and may be either directly displaced by the action of the locking bar or be indirectly displaced as by other vibration because the boards are free to move when the overall locking bar is removed.
In accordance with one embodiment of the present invention, these and other difficulties and problems are obviated by providing a novel strip type multi-contact connector for communicating with a plurality of spaced apart conductive pads or terminals carried on a circuit board which in turn supports a number of interconnected electronic components. Each contact or contact member of the multiplicity included in the connector assembly takes the form of a specially cut and shaped round spring wire constituting a pair of individual wire contact units extending generally in parallel relationship to one another but each being of a different length. Each unit comprises a substantially arcuate shaped contact element or beam portion cantilevered from one end of a resilient arm while the opposite ends of the arms are integrally joined to form a loop adapted to serve as a connection point to which a lead wire may be readily attached. Since the contact includes a pair of cantilevered contact elements, each contact possesses redundant points or areas of contact for greater reliability. Each contact of the multiplicity is supported by and within a different one of a plurality of co-extending slots and passageways formed in a relatively rigid, but somewhat flexible, strip-like insulative support member which is mounted on a flat pad on the mating surface of a circuit board. This construction provides a solid locking-in of the contacts by combining both a pressure and a sliding motion between the arcuate contact element of each unit of the connector contact and a circuit terminal located on the circuit board with an exceedingly low electrical contact resistance and provides enhanced reliability under vibration conditions. A feature of the present invention resides in the provision of a grounding strip as a part of the connector assembly which extends along the length of the connector support strip and which is in engagement with the fiat pad on the circuit board when the connector strip is mounted thereon. Also another feature of the invention resides in so forming the contact unit and mounting the same in the slotted strip that the free ends of each contact unit normally lie within a respective slot. In this way the con nector unit is protected from being inadvertently bent when handling the connector.
Therefore, it is a primary object of the present invention to provide a novel strip type multi-electrode connector which combines pressure and a sliding motion to provide extremely reliable electrical and mechanical contact.
It is another object of the present invention to provide a novel electrical connector which requires no compromise between wear-resistant plating for the contacts incorporated into the connector and that surface against which the individual contacts are forcibly urged and which provide an effective electrical conduction across the boundary.
Still another object of the present invention is to pro vide such an electrical connector as described above which is not susceptible to contact damage due to false or misaligned insertion of a connector assembly with a circuit board.
Another object of the present invention is to provide a novel electrical connector assembly which includes a rigid strip for mounting a plurality of contacts which is, by positive latching, locked in place on a circuit board independently and without auxiliary locking bars or the like.
It is another object of the present invention to provide such an electrical connector assembly in which the circuit board or panel, when deliberately released, is totally free and requires no additional force as from sliding contact friction during Withdrawal or removal.
Still a further object of the present invention is to provide a novel strip connector assembly, including a grounding strip carried thereon, which is compact and permits high density stacking or arrangement of the contact elements in a line with respect to one another and that is inexpensive to manufacture.
The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
FIGURE 1 is a plan view of the strip connector assembly having a plurality of contacts incorporating the present invention and illustrating the connector assembly prior to attachment to a supporting circuit board;
FIG. 2 is a perspective view, in section, of the connector strip shown in FIG. 1 taken in the direction of arrows 2--2;
FIG. 3 is a side elevational view of a contact having contact redundancy characteristics illustrating the beam portion of each connector unit as employed in the connector strip of FIG. 2; and
FIG. 4 is a plan view of the contact shown in FIG. 3 illustrating the pair of individual connector units.
Referring to FIG. 1(a), there is shown a portion of an etched or printed circuit board 9 for supporting a connector strip 10 to complement the novel electrical connector as shown in FIG. 1(b) in accordance with the present invention. The connector strip is illustrated in an inverted position for purposes of clarity; however, it is to be understood that when assembled with the circuit board the strip as shown will be turned over as will become more apparent from the following description.
The board 9 in this example is substantially rectangular and has a linear edge marginal region 11 carrying a flat pad 12 of suitable electrical conductive material presenting a mounting surface on which the connector strip is placed. Arranged in spaced parallel relationship to the pad and the edge marginal region of the board, there is disposed on the face of the board a plurality of electrical conductive areas or circuit terminations 13 which may be etched or otherwise formed on the board face and which communicate with other circuitry (not shown) on the board. The board 9 has a pair of ends 14 (only one end shown) which are substantially orthogonal to the edge marginal region 11. Formed between the ends 14 and in an area 15 between the pad and the row of electrical terminals, there is located a plurality of attachment holes, such as hole 16, which register with similar holes provided in the connector strip 11 to permit the passage therethrough of suitable retaining or fastener means (not shown) such as bolts, screws or the like.
The connector strip shown in FIGS. 1(1)) and 2 includes an elongated member 17 which may preferably be formed, as by molding from lightweight electrically insulative plastic materials or similar electrically nonconducting material. The material is relatively rigid, but somewhat flexible so that the connector strip will mate properly with the circuit board surface and, in effect, he self-compensating for any surface irregularities existing between the mating parts. Member 17 comprises, in general, a support portion or base 18 having an upper surface 20 and an under surface 21 adapted to engage with the mounting surface carried on the circuit board. The under surface 21 is provided with a recess 22 formed in a trailing edge portion or flange 23 for accommodating the mounting of a grounding strip 24. The flange extends rearward of the member beyond the rear extremity of the support base so that when the connector strip is assembled on the circuit board the flange projects over the pad 12 placing the grounding strip in mating contact with the pad.
The grounding strip may be composed of any suitable electrically conductive material; however, a Wire mesh or webbing is illustrated which is folded over and suitably secured to the member flange by conventional means such as adhesive, rivets, fasteners or the like.
Member 17 is further provided with a plurality of open ended, spaced apart passageways, such as passageways 25, whivh extend along the strip in a row normal to the longitudinal axis of the strip so that each passageway is in direct alignment with one of the electrical terminals carried on the circuit board. One end of each passageway terminates from the member 17 at the rear of the supporting base beneath the member flange while the opposite end of each passageway terminates into a slot 26 contiguous therewith which opens through the under surface 21. Such construction provides a shoulder 27 where the passageway merges with the terminating end of the slot. If desired, member 17 may be constructed from two separate parts which may be represented by the base 18 and the portion of the strip carrying the flange and formed slots which may be mounted on the base and held together by means of the fasteners employed to mount the strip on the circuit board.
As previously mentioned, the member 17 has incorporated therein mounting holes such as hole 28 which register with the attachment holes 16 of the circuit board for readily securing the strip together with the circuit board to complete the assembly.
Disposed within each passageway along the length of the connector stn'p there is provided a resilient self-biasing contact 30 as illustrated in FIGS. 3 and 4. Each contact of the multiplicity is preferably formed from a round spring wire of approximately /2 inch to in in length and preferably composed by beryllium copper. Preferably, the wire diameter may be in the order of .010 inch in diameter and heat treated for one hour at 500 F. if beryllium is employed, to assure reliable spring action and desirable elasticity. Inasmuch as it is desirable to use a strong elastically bendable material which is generally not considered particularly suitable for providing the best and most reliable contacts the contact wire 30 is plated with approximately 50-100 millionths of an inch gold plating. The contact wire is suitably cut and bent about a point on either side of its mid-section to form a loop or head 31 between its opposite ends so as to provide a pair of co-extending individual contact units 32 and 33 extending generally in parallel relationship and being of different lengths. Each individual contact unit includes a contact element or "beam portion 34 and 35 cantilevered from resilient arms 36 and 37 respectively via an intermediate section 38. Each contact element substantially takes the form of an arcuate bend or shape having an outwardly facing terminal engaging area 40 and terminating at its free end in a reverse curved section 41 having a strip base engaging area 42. Inasmuch as each contact unit is of a different length, each element or beam length, that is from points A to B and points A to D, have a different spring rate and a different natural resonant frequency, and thus, a greater reliability under vibration conditions. Inasmuch as two points of contact, as represented by numeral 40, are employed for each contact 30, the construction of the contact possesses a feature of redundancy for greater reliability. It should also be noted that the contact 30 is a single, continuous piece, thus affording the most reliable electrical continuity.
Assembly of the contact 30 into the slot of the support block is effected by inserting point G representing the bent portion of the mid-section of wire of the contact into the slot and sliding the contact through the passageway until section 38 rests against the shoulder 27 of the support block. The resilient arms of the contacts are bent back at approximately a 45 angle at point P to achieve locking of the contact into the block. Once the contact has been locked into position, the terminal engaging areas 40 of the cantilevered contact elements project through the slot above the surface 21 while the sections 42 reside within the slot so that the strip side walls which define the slot protect the cantilevered contact element from inadvertent damage which may otherwise occur through mishandling of the connector. If the contact were damaged at any time, it would be a simple matter of reversing this procedure to remove the damaged contact, and a new contact would then be inserted. It is to be noted that the basic contact is formed from point A outwardly to the ends represented by points C and E and that, as in many other contacts, the configuration of the back end represented by point G is subject to numerous modifications to make the contact adaptable for receiving and making connection with lead wires such as by suitably mounting a sleeve, terminal, or the like.
In using the contact strip of the present invention, the strip may be of whatever desirable length is required. The strip may be trimmed to any shorter length, either during or after manufacture of the basic strip. Once the length has been determined, and if the desired length is shorter than the manufactured strip, the strip may be severed anywhere along its length to the desired dimension. Next, the connector strip is laced on the circuit board 9 so that the grounding strip 24 of the support block rests on the pad 12 and fastening holes 16 and 28 placed in registry to accommodate the installation of a suitable fastener. The ends of the plurality of contacts 30 represented by point G will readily accommodate the attachment of additional circuitry leads so that adequate electrical and mechanical communication exists. The connector strip and the circuit board are now assembled and the contact elements or beam portions of the individual contacts are in communication with the terminals on the circuit board.
As the connector strip is pressured into contact with the terminals of the circuit board, each individual half or contact unit of the contact, upon being mounted, undergoes two deflections. The first deflection occurs from point A to points B and D, and secondly, as points C and E contact the support strip or block base approximately .010 inch before full compression of points B and D (which occurs when points B and D are flush with the mounting surface of the support strip). Such construction provides a very solid lock-in of the contacts, with an exceedingly low electrical contact resistance and enhanced reliability under vibration.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. An electrical connector comprising:
a semi-rigid backing strip of electrically insulative material having a plurality of co-extensive slots and passageways arranged in parallel relationship along the length of said strip; and
a specially cut and shaped round spring wire located withing each of said plurality of slots and passageways constitutinga pair of individual wire contact units extending generally in parallel relationship to one another and each contact unit being of different length;
said contact units of each of said wires constituting arcuate shaped contact elements located in each of said slots and being cantilevered from one end of a resilient arm located in each of said passageways whereby terminal engaging portions of said contact elements project equally above the surface of said backing strip exteriorly of said slot, the free end of each cantilevered contact element terminating in an arcuate section having a reverse curved shape from the shape of said contact element and having a surface area adapted to slidably engage with said backing strip within said slot upon the application of pressure upon said projecting portion of said contact element;
said backing strip including a flange extending along the length of said backing strip and having a recess formed in the surface thereof on the same side of said backing strip through which said contact elements project, and further including a grounding strip of electrically conductive material secured to said flange within said recess.
2. The invention as defined in claim 1 wherein said projecting portions of said contact elements and said grounding strip are adapted to engage a plurality of circuit terminals and a pad on a circuit board, and further including fastening means for detachably coupling said backing strip to said circuit board whereby said contact elements and said ground strip are held under pressure into engagement with said terminals and said pad respectively.
3. The invention as defined in claim 1 including an intermediate section formed from said wire in each of said contact units and being integrally joined at a location adjacent the merger of said slot with said passageway in each of said plurality by its opposite ends to said arm and said contact element respectively, and the opposite end of each arm to its end joined with said intermediate section terminating in a bent section extending beyond the termination of said pasageway so that each contact member is retained on said backing strip by the cooperative holding action of said intermediate section and said bent section.
4. A connector assembly carrying at least one contact member and adapted to be pressed into abutting engagement with a substantially fiat surface of a circuit board for electrically connecting said contact member to a conductive area of said circuit board surface, said assembly comprising:
a backing strip having a first substantially flat surface adapted to be pressed into intimate abutting engagement with a substantially flat circuit board surface, said backing strip defining a slot therein extending inwardly from said first surface and terminating at a bottom slot surface;
a spring contact member including a mounting portion,
a first beam portion cantilevered from said mounting portion, a first contact portion extending from said first beam portion, and a first free end portion extending from said first contact portion; and
means securing said spring contact member mounting portion in said slot with said first contact portion extending beyond said backing strip first surface and said first free end portion being spaced from said bottom slot surface, said first contact portion extending beyond said backing strip first surface by a distance greater than said spacing between said first free end portion and said bottom slot surface whereby said circuit board flat surface will engage said first contact portion and force said first free end portion against said bottom slot surface as said backing strip first surface is pressed toward intimate abutting engagement with said circuit board surface;
said contact member including a second beam portion cantilevered from said mounting portion, a second contact portion extending from said second beam portion, and a second free end portion extending from said second contact portion;
said second contact portion extending beyond said backing strip first surface and said second free end portion being spaced from said bottom slot surface, said second contact portion extending beyond said backing strip first surface by a distance greater than said spacing between said second free end portion and said bottom slot surface whereby said circuit board flat surface will engage said second contact portion and force said second free end portion against said bottom slot surface as said backing strip first surface is pressed toward intimate abutting engagement with said circuit board surface;
said first and second beam portions being of different lengths to thereby define dilferent spring rates;
said first and second contact portions extending beyond said backing strip first surface by substantially the same distance.
5. The assembly of claim 4 wherein said contact portions and said free end portions are shaped in the form of curves opening in substantially opposite directions.
6. The assembly of claim 4 wherein said means securing said mounting portion in said slot includes at least one shoulder surface on said backing strip extending substantially perpendicular to said backing strip first flat surface, said contact member mounting portion abutting said shoulder surface to thereby substantially prevent relative movement between said mounting portion and said backing strip.
7. A connector assembly carrying one or more contact members and adapted to be pressed into abutting engagement with a substantially flat surface of a circuit board for electrically connecting said contact member to a conductive area of said circuit board surface, said assembly comprising:
a backing strip having a first substantially flat surface adapted to be pressed into intimate abutting engagement with a substantially fiat circuit board surface, said backing strip defining a slot therein extending inwardly from said first surface and terminating at a bottom slot surface;
a spring contact member including a mounting portion,-
a first beam portion cantilevered from said mounting portion, and a first contact portion extending from said first beam portion; and
means securing said spring contact member mounting portion in said slot with said first contact portion extending beyond said backing strip first surface whereby said first contact portion will engage and subsequently slide along said circuit board surface as said backing strip first surface is pressed toward intimate abutting engagement with said circuit board surface;
said contact member including a second beam portion cantilevered from said mounting portion and a second contact portion extending from said second beam portion;
said second contact portion extending beyond said backing strip first surface whereby said second contact portion will engage and subsequently slide along said circuit board surface as said backing strip first surface is pressed toward intimate abutting engagement with said circuit board surface;
said first and second beam portions being of different length to thereby define different spring rates;
said first and second contact portions extending beyond said backing strip surface by substantially the same distance.
References Cited UNITED STATES PATENTS 1,828,276 10/1931 Beers 339-176 2,396,725 3/1946 Thomas 339-59 2,433,358 12/1947 Garberding 339-220 XR 3,040,291 6/1962 Schweitzer et al. 339-176 FOREIGN PATENTS 1,147,643 4/1963 Germany. 866,052 4/1961 Great Britain.
MARVIN A. CHAMPION, Primary Examiner P. A. CLIFFORD, Assistant Examiner U.S. Cl. X.R.