US 3649743 A
A wrapped wire connection in which an elongated post having at least one sharp edge is wrapped with a standard insulated wire and an outer sleeve fits over the wrapped turns of the wire to apply, at least temporarily, mechanical pressure to the wrapped wire, causing the sharp edge of the post to pierce the wire insulation and thereby to form a permanent electrical and mechanical connection.
Description (OCR text may contain errors)
United States Patent OLoughlin  WRAPPED WIRE CONNECTION Mar. 14, 1972 3,014,140 12/1961 Tupper ..339/97 R x 3,071,750 1/1963 Heselwood ..339/97 R 3,243,501 3/1966 Patrick et al. 1 74/94 R x Primary Examiner-Darrell L. Clay Attorney-Thomas M. Marshall I 7] ABSTRACT A wrapped wire connection in which an elongated post having at least one sharp edge is wrapped with a standard insulated wire and an outer sleeve fits over the wrapped turns of the wire to apply, at least temporarily, mechanical pressure to the wrapped wire, causing the sharp edge of the post to pierce the wire insulation and thereby to form a permanent electrical and mechanical connection.
7 Claims, 6 Drawing Figures PLAST/C OE S/A/TEEED MET/ 7L P/VQT/CLES PAIENTEDHARM I972 8,649,743
INVENTOR. FQAA/t/S 40200010 A TTORNE BACKGROUND OF THE INVENTION This invention relates to a new and improved mechanical and electrical connection between an electrical terminal and a conductor. It relates specifically to an improved solderless connection in which a wire conductor is wrapped around a terminal post.
There are several methods by which electrical components are fixed to printed circuit boards and the like, among those methods being the use of crimpable electrical connectors which mechanically and electrically interconnect the pins or terminal electrical points of circuit components. In many cases, the component, such as an integrated circuit pack, has pins that are inserted into holes in a socket or other terminal on the printed circuit board. In some of the prior art techniques, the printed integrated circuit component is carried by a special receptacle that is received within the holes of the circuit board. The present invention provides a new connection to the terminals of such components by flexible wire conductors.
Once components are mechanically secured to the circuit board, wire leads are attached to terminal posts for connection to other circuit boards or distant components. Where possible, solderless connections are often used, the most common of which is the wrapped wire connection whereby the connecting wires and leads from the circuits are wrapped around upstanding terminal posts. In this case, of course, the wire conductor leads wrapped around a single post may originate from one or more electrical components.
The concept of wrapping an electrical conductor around a terminal post is, of course, an old technique that has been used for several years. One of the disadvantages of this technique, however, is that, alone, it cannot be used to connect insulated wire to the terminal, unless the insulation is first stripped away before making the connection. In order to connect a stranded insulated wire to a terminal post, it has been the usual practice first to strip the insulation from the wire end and then to solder the wire to the terminal. Wire wrapping methods have not been possible in such cases, particularly if the wire is at all delicate or of small gauge, because the individual strands tend to separate and break during winding. Fine solid wires, of course, also may rupture during attempted winding, especially if the terminal post has a small cross section, requiring turns of extremely small diameter. For these reasons, it has been considered more reliable to solder such small gauge wires to the post or to use other types of connections to the post, in any case it being necessary to strip the insulation prior to connection.
SUMMARY OF THE INVENTION In accordance with the invention these and other disadvantages of earlier practices are remedied by the improved wrapped wire electrical connection described herein, which provides wrapped wire connection to a terminal post without stripping the insulation from the wire conductor. In brief, this connection comprises a conductive terminal post, preferably having at least one sharp edge, extending in the lengthwise direction of the post, at least a partial turn of the insulated conductor wrapped about the post, and an outer sleeve fitting over and partially surrounding the turns of the wrapped conductor to apply, at least temporarily, a mechanical pressure to urge the conductor against the post and to cause the post to pierce the insulation for electrical contact of the post and the conductor. In a preferred embodiment, the sleeve is constructed from a powdered metal material having a low plastic memory such that it can be crimped into close proximity to the wrapped conductor to force it against the sharp edge of the post, but which can be broken away from the post to repair the connection, if necessary, by applying, for example, a moderate stress to the outside of the sleeve.
Because the insulation remains on the wire conductor during the wrapping operation, the insulation sleeve, in the case of plastic or fabric materials, provides strain relief for the conductor. That is, the insulating sleeve carries and relieves the wire conductor of tension and other loads that otherwise would be applied directly to the conductor. Furthermore, by leaving the insulation on the wire end throughout the connecting operation, stranded wires may be wrapped as easily as solid conductor wires.
BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be made to the following detailed description of preferred embodiments and to the accompanying drawings, in which:
FIG. 1 is a partial perspective view ofa circuit board having terminal posts to which wire conductors are connected in ac cordance with the invention;
FIG. 2 is a plan view ofa connection according to the invention;
FIG. 3 is an elevational view in partial cross section of the connection of FIG. 2;
FIG. 4 is a plan cross-sectional view, showing the connection of FIGS. 2 and 3 after the outer sleeve has been deformed into close contact around the conductor turns;
FIG. 5 is yet another form of outer sleeve suitable for use in the invention; and
FIG. 6 is a plan view of a rectangular terminal post and sleeve according to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 illustrates one manner in which the present invention may be found in practice. There, an insulated printed circuit board 11 is shown to include an electronic component, such as an integrated circuit pack 13 (or socket for such a component) that has terminal posts or pins 15 as terminals extending through apertures in the circuit board 11. Wire conductors 17 used for interconnecting the circuit component 13 with other components are wrapped in a series of close helical turns around the terminal post 15 and, in accordance with the invention, sleeves 19 are placed over at least some of the turns ofthe wire conductor 17 and (preferably) crimped.
FIGS. 2 and 3 depict the wrapped wire connection in greater detail. As illustrated, the post 15 extending through the circuit board 11 has a square cross-sectional configuration and is wrapped with several closely spaced turns of the wire 17. The method of wrapping terminal posts in this manner is well known in the art and may be accomplished by hand, by special tool or by machine. As already mentioned, one of the problems with merely wrapped connections is that they could not be readily applied to stranded wire and, moreover, if the conductor was an insulated conductor having, for example, an insulating varnish or plastic coating, the insulation must be stripped from the conductor prior to wrapping. In accordance with the invention, however, the sleeve 19 fits closely around the wrapped turns of the conductor 17, as is best seen in FIG. 2. When the sleeve is inserted over the turns, they are pressed against one or more of the sharp corners 15a of the post. Generally, the sleeve must be deformed radially, as by squeezing, to apply sufficient pressure to the wire to cause the post to pierce the insulation on the conductor 17. On the other hand, varnish coating insulation can sometimes be pierced if the sleeve alone fits tightly about the turns. In either case, the post thus makes electrical contact and intimate physical contact with the conductor.
After the sleeve 19 has been placed over the conductor wrapped post, it is preferable to crimp it. FIG. 4 is a cross-sectional view through the connection following crimping. As shown there, the sleeve 19 has been deformed to squeeze the wrapped turns of the conductor 17 around the post 15 and thereby obtain a very secure electrical and mechanical connection.
As summarized above, the sleeve can be constructed of various materials, both dielectric and conductive. Sintered powdered metal sleeves are adaptable to crimping, if required,
and can be broken away easily thereafter if the connection is to be repaired or replaced merely by applying lateral pressure to the sleeve. Plastic sleeves are also suitable, as are sleeves constructed from yet other materials that can be made to contract or deform radially into tighter contact about the wire turns.
it is preferred in any case that the sleeves possess a coefficient of thermal expansion in the radial direction that is not appreciably different than the corresponding coefficient of the post and/or turns so that the sleeve tends to stay in close contact to the wrapped wire. When temperatures only higher than the assembly temperature are expected, this coefficient may be selected to be smaller.
FIG. 5 indicates an alternate form of sleeve 21, which is cylindrical in shape and is formed with a slot 23 cut at an angle to the axis through the wall of the sleeve. The sleeve in this case is constructed from a resilient material and may be dimensioned slightly undersize so that it fits extremely tightly over the wrapped turns of the conductor. The slot 23 enables the sleeve 21 to expand to accommodate the wrapped turns and yet continue to apply force urging the turns against the post. As in the case ofthe continuous sleeve, the slotted sleeve 21 may be crimped, or deformed, by any suitable tool to form a permanent mechanical and electrical connection.
An electrical connection according to the invention, can, of course, be used with any post geometry. FIG. 6 shows a thin rectangular post 25 and an associated oval-shaped sleeve 27. In some cases it may be desirable to make the clearance gap 28 between the corner of the post 25 and the sleeve 27 of a slightly smaller dimension than the diameter of the wire surrounding the post. If the insulation of the wire is of the varnish type, for example, this can ensure the application of enough radial force to cause the insulation to be pierced by the post merely by placing the sleeve over the post. On the other hand, where the sleeve is positioned by hand or where it must be placed over the wrapped conductor without moving any of the turns, it is preferable to have the clearance gap 28 slightly larger than the wire diameter. In such cases, of course, the sleeve must be crimped following its placement over the wrapped turns.
Although the invention has been described with reference to particular embodiments, yet other variations, embodiments and modifications may occur to those skilled in the art. For example, several types of materials may be used in the construction of the sleeve and the post may take on any geometry operable to effect the electrical connection through insulated wire. Thus, all such embodiments, variations and modifications are intended to be included within the scope of the appended claims.
What is claimed is:
l. A wrapped wire electrical connection for improved mechanical and electrical interconnection of a terminal and an insulated wire, comprising:
a conductive post providing a terminal for an electrical connection, said post having at least one sharp corner extending lengthwise thereof;
an insulated wire conductor at least partially wrapped around the post and crossing said sharp corner; and
a sleeve overfitting said wrapped conductor and applying a mechanical pressure thereto urging said conductor against the post causing the sharp corner of said post to pierce the insulation and electrically contact the conductor.
2. A connector according to claim 1, in which:
the sleeve is radially deformed inwardly to surround said wrapped conductor.
3. A connection according to claim 2 in which:
the sleeve is formed of sintered powdered conductive material having a low plastic memory.
4. A connection according to claim 1, in which:
the sleeve is radially resilient and resiliently urges the wrapped conductor against the post.
5. The connection as set forth in claim 1, in which:
the sleeve is comprised ofa plastic material. 6. A connection according to claim 1, m which:
the sleeve has a coefficient of expansion in the radial direction that is approximately the same as the corresponding coefficient of the post and wire as a unit.
7. A method for making an electrical connection of an insulated conductor to a conductive terminal post having at least one sharp corner extending lengthwise thereoft'or piercing the insulation ofsaid insulated conductor comprising:
wrapping at least a partial turn of the insulated conductor around the post to include crossing the sharp corner thereof;
surrounding the wrapped connection with a deformable sleeve; and
deforming said sleeve in a radially inward direction causing the sharp corner of the terminal post to pierce the insulation and electrically contact the conductor.