US3511921A - Indium coated slotted electrical connectors - Google Patents

Description

y 1970 J. P. PASTERNAK 3,511,921

INDIUM COATED SLOTTED ELECTRICAL CONNECTORS Filed Nov. 1, 1968 lNl/ENTOR J I? PASTERNAK E L W A TTORNEV J. P. PASTERNAK INDIUM COATED SLOTTED ELECTRICAL CONNECTORS 2 Sheets-Sheet 2 ALUMINUM WIRE- INDIUM PLATE INTERFACE O O m a c E 0 A 6 L IT P 0 OT M mo w m W I S G I a C F Y lmv C P M E T May 12, 1970 Filed Nov. 1, 1968 2535 8558a 561 2:5 z megs;

United States Patent 3,511,921 INDIUM COATED SLOTTED ELECTRICAL CONNECTORS John P. Pasternak, Plainfield, N.J., assignor to Bell Telephone Laboratories, Incorporated, Murray Hill, N.J.,

a corporation of New York Filed Nov. 1, 1968, Ser. No. 772,706 Int. Cl. H01r 9/08 US. Cl. 174-88 10 Claims ABSTRACT OF THE DISCLOSURE In a wire connector, slotted posts strip the insulation and grasp the conductors of insulated wires that are forced into respective slots in the posts. The posts are interconnected and coated with indium at the slots. A frame holding the wires guides them into the slots. A case holds the posts and grips the frame to form a protective shield.

Background of the invention This invention relates to solderless electrical connectors, and particularly to so-called slotted connectors for permanently connecting one insulated. wire to another.

Such slotted connectors are composed of inter-connected bifurcated posts. The wires to be connected are placed at the open end of the slots between the beam-like bifurcations and forced into the slots. The slots are narrow enough so that while the wire is being forced into them, the bifurcations strip the wires insulation and bear into the surface ofthe wires conductor. The bifurcations apply a continuous force against the wire and thus maintain a permanent connection.

While such connectors have been successful for most purposes, they introduce undesired resistances after they have been subjected to repeated temperature cycles. In the field of telephony, where the connections are expected to serve over a 40-year life span, the cumulative resistances of many connections in series can create undesirable noi'ses. With copper wire the added resistances are small and the added noise often acceptable. However, with aluminum wires whose oxide surfaces add more undesired resistances, the noises created are frequently intolerable.

Also, aluminum wires weaken at the connection. Thus, if they are subject to flexure, aluminum wires tend to break.

The invention According to a feature of the invention these deficiencies are overcome by coating the surface of the posts at the slots with a non-oxidizing, solid but readily flowable, conductive material that penetrates the microscopic cracks in the aluminum oxide films to establish contact with the pure aluminum of aluminum conductors. According to another feature of the invention, the material is indium.

The softness and ductility of indium allow it to be easily displaced by the high spots or asperities of the conductor. The indiums displacement tends to form a gas tight seal between the conductive member and itself. This reduces oxidants at the interface. The indium is self-annealing and does not work under compression.

According to yet another feature of the invention the Wires are forceably inserted onto the slots by holding the wires parallel to each other in an insulated frame, and by pressing the frame onto the posts. Preferably the frame has recesses transverse to the wires and aligned to receive the posts.

According to still another feature of the invention, a trough-shaped base supports the posts interiorly and grasps the frame when it is pressed onto the posts so as to form a secure connection.

According to still another feature of the invention damming walls astride the posts in the base confine an encapsulating compound to the post area. Preferably, the frame has recesses to receive these walls and the walls are slit for grasping the wires.

According to yet another feature of the invention move ment of the wire relative to the connection is restrained by offsetting the wires about projections on the frame and by holding the wire insulation in the walls slits.

These and other features of the invention are pointed out in the claims. Other objects and advantages of the invention will become evident from the following detailed description when read in light of the accompanying drawrngs.

Brief description of the drawings FIG. 1 is an exploded perspective view illustrating a connector embodying features of the invention;

FIG. 2 is a perspective exploded view illustrating the connector of FIG. 1 with the wires in place in the frame;

FIG. 3 is a partly sectional plan view of FIG. 2;

FIG. 4 is a partly sectional elevation of FIG. 2;

FIG. 5 is a perspective view showing in detail: the contact between conductors and posts of FIG. 1;

FIG. 6 is a section showing details of the interface between a conductor and post of FIG. 1;

FIG. 7 is a graph illustrating the differences in the increase of joint resistances resulting from differences in plating materials of a post in FIG. 1 after a number of temperature cycles;

FIG. 8 is an enlarged sectional view of the surfaces of two aluminum conductors in contact with each other; and

FIG. 9 is an enlarged sectional view illustrating the indium plate interface between an aluminum conductor and an indium plated conductor such as the post in FIG. 1.

Description of preferred embodiment In FIGS. 1 to 4 the connector embodying the invention is composed of a contact assembly 8 snap fittable onto and about a wire frame 10. The frame 10 receives one of the wires 12, whose aluminum conductor 14 is to be connected by the connector, in a plastic U-shaped and elongated frame section 16. A blind bore 18 which is shown most clearly in FIG. 3 extends parallel to the U-shaped section 16. The bore 18 receives a wire 20, whose aluminum conductor is to be conected to the conductor 14 by the connector. The wires 12 and 20 emerging from the section 16 and the bore 18 are offset around two T-shaped projections 22, which in effect bind the comparatively stiff wires so as to hinder their longitudinal and lateral motion. A pair of slits 26 and 28 extend through the frame 10 and terminate at a twenty mil thick plastic coverplate 29 integrally molded to the top surface of the frame 10.

When the frame 10 is snapfitted into the assembly 8, the slits 26 and 28 receive four bifurcated posts 30, 32, 34, and 36 extending from a common member 38 and forming respective funnel- shaped slots 40, 42, 44, and 46. The posts and the common member 38 constitute a conductive C-shaped connecting unit 48 that is bonded to form an integral part of the assembly 8.

The bifurcations of the posts 30, 32, 34, and 36 form beams astride the respective slots 40, 42, 44, and 46. The beams of posts 30 and 36 conductively clasp the conductor 21 in their respective slots 40 and 46 through breaks in the insulation on the wire when the wire frame 10 is snapfitted into the assembly 8. The beams of the posts 32 and 34 conductively clasp the conductor 14 in their respective slots 42 and 44 and through breaks in the insulation on the wire 12. The unit 48 thus connects the conductors 14 and 21 as the posts clasp the conductors. The posts clasping the conductors are shown in FIG. 3 which illustrates the assembly 8, frame 10, wires 12 and 20 snapfitted together. A one mil coating of indium which has been electroplated on the unit 48 covers surfaces of the unit. At the slots 40, 42, 44, and 46 the indium intervenes between the conductors 14 and 21 and the copper substrate of the posts 30, 32, 34, and 36.

In the contact assembly 8, the unit 48 is bonded to the base of a hollow plastic or nylon trough 50'. The frame snapfits into the trough 50. A pair of ears 52 and 54 extending outwardly from the trough 50 grasp the T-shaped projections 22 and 24 of the frame 10. A pair of slits 60 and 62 parallel to the slits 26 and 28 on the frame 10 receive two plastic damming walls 64 and 68 molded to stand up on the base of the trough 50. Four cuts 70, 72, 74, and 76 in the damming walls are aligned with the slots 40, 42, 44 and 46 and grip the insulation on the wires 12 and 20. A rubber-compound encapsulant 80 is retained within the area of the posts 30, 32, 34, and 36 between the damming walls 60 and 68 and the side walls of the trough 50.

To make a connection between the conductors 14 and 21 of the wires 12 and 20, a craftsman separates the two separable portions of the connector, namely, the frame 10 and the assembly 8. He fits the wire 12 into the U- shaped section 16 and around the T-shaped projections 22 and 24 as shown most clearly in FIG. 2. He then pushes the wire 20 through the blind bore against the end of the blind bore and twists the outer end of the wire around the T-shaped projection 22, again as shown in FIG. 2. Olfsetting these wires around the T-shaped projections restrains movement of the wires longitudinally and laterally. Then he presses the entire assembly of wires and frame 10 into the trough 50.

The pressing action forces the encapsulant 80 to flow upwardly trough the slits 60, 26, 28, and 62 as the frame enters the trough 50. The pressing action also forces the previously positioned wires past the flared openings of the funnel-shaped slots 40, 42, 44, and 46. The bifurcations of the posts 30, 32, 34, and 36 tear into the comparatively soft plastic insulation on the wires 12 and 20 as the frame 10 forces them further into the slots. The slots are sufliciently narrow so that after tearing into the insulation they encounter conductors 14 and 21. As the wires 12 and 20 are forced further into the slots 40, 42, 44, and 46, the conductors 14 and 21 which are harder than the insulation tend to spread the beam-like bifurcations of posts 30, 32, 34, and 36 as they embrace the conductors. However, the posts are sufliciently rigid so that as the wires pass into the slots the posts scrape a portion of the conductors surfaces.

When the motion of the wires into the slots ceases, the posts 30, 32, 34, and 36 continue to press inwardly to ward the slots and against the conductors 14 and 21 by virtue of the beamlike resilience exhibited by the copper or brass substrate material of which the unit 48 is largely composed. At the same time, the encapsulant 80* flows around the contact area between the posts and the wires through the; slots 60, 26, 28, and 62 to encapsulate the entire connected area. The damming walls 64 and 68,

serve to prevent too much encapsulant from escaping outside the confined areas.

Without the damming walls, sufficient encapsulant must be provided to fill the entire trough 50' and would result in considerable encapsulant flowingout of the connection during the connecting operation and create problems of cleanliness. The damming walls 64 and 68 also serve the function of grasping the insulation of the wires 12 and 20 in the slits 70, 72, 74, and 76 so as to reinforce the restraining action of offsetting the wires 12 and 20 around the projections 22 and 24.

As the indium contacts the aluminum surfaces of the conductors 14 and 21, it flows into the interstices between the oxide coating which may remain or form on the conand as the slots scrape portions of the aluminum surface away and break the oxide coating. 1

FIG. 5 illustrates in detail the contact formed between the posts 30, 32, 34, and 36 and the conductors 14 and 21 of the wires 12 and 20.

The indium on the posts has a softness and a ductility which allows it to be easily displaced by the microscopic high spots or asperities on the aluminum conductor. This allows an increased contact area between the conductor and the indium and between the indium andmetal below as the asperity pushes into the indium. The indium has a low elastic limit, and, because it is self-annealing, does not work harden under compression. The indiurn penetrates the voids or cracks in the aluminum oxide film when the loading pressure is sufficient only to partially fracture the film. FIG. 6 illustrates a detailed cross section of the interface between an indium-plated post such as 30 and an aluminum conductor such as 21 showing the indiumaction as the wire is forced between the bifurcations of the post 30. FIG. 7 is a graph which illustrates the increase of mean omt resistance in milliohms as a result of subjecting a connection between an aluminum wire and an indium plated post as shown in FIG. 5 to repeated temperature cycles from -40 C. to +60 C. The graph also shows a similar connection formed with a tin-plated post and an aluminum wire. As can be seen from the graph, the connection using an indium-plated post, displayed little or no mcrease in mean joint resistance whereas the tin-plated post exhibited a much higher increase in joint resistance. In fact, after about 200 temperature cycles, the increase with tin plate was almost 5 6 times as great as the increase with indium-plated posts.

FIGS. 8 and 9 compare the manner. in which aluminum conductors 84 and 86, coated with oxide 88, contact each other, and the way an indium plating penetrates micro scopic breaks in the oxide surface 92 of an aluminum conductor 94 to establish the contact betwee'n the aluminum conductor and the copper substrate96 of a post. This tween the bifurcations of the posts increasesfsince the working tends 'to create such microscopic breaks in the aluminum surface. 1

The advantages of the invention are augmented by the projections 22 and 24 snubbing any tensile pulls upon the wire. These projections impart offsets to the wires 12 and 20 so as to absorb any pulls that are placed upon the wire during operation or during placement or connection. Such pulls may readily occur when a splice is formed in a cable containing hundreds of wires such as 12 and 20 to be connected. Assisting this absorption are the damming walls 64 and 68 which grasp the wires 12 and 20 by means of their slits. As a result, the tensile strength of the wire is maintained and the contact stability of the connection is maintained. The damming walls 64 and 68 are particularly useful for restricting side to side movements of the wires. i

The damming walls 64 and 68 also minimize wash-out i and work-out of the encapsulant from the area of the plated portion of the contact. They also restrict wire movement and restrict exposure of the conductor portions of the contact within the connection.

One embodiment of the invention involves making the I slots 40, 42, 44, and narrower at the closed ends than i vention resides in the projections 22 and 24 holding onto.

the offset wires 12 and 20 as a connection is being made. This is of great importance in cases where several hundred such connections must be made to form a cable splice. As such, craftsmen must work with many connectors and the ability to fit the frame onto the wires where it will remain without falling away until the frame is capped with the assembly 8 substantially increases the speed of making connections.

Also, pressing the frame 10 into the assembly 8 can be done by hand or with a simple tool rather than with complicated tools hereto used for this purpose. Such tools often required alignment means for aligning the wire with the slots. In this case, the connectors themselves furnish the alignment.

According to one embodiment of the invention the indium electroplated on the surfaces of the unit 48 has a purity in excess of 99.994%.

While an embodiment of the invention has been disclosed in detail, it will be obvious to those skilled in the art that the invention may be practiced otherwise without departing from its spirit and scope.

What is claimed is:

1. A wire connector comprising, rigid conductive means, said conductive means forming a pair of slots each being narrower than the conductor of a wire to be connected, said conductive means being sufiiciently resilient so that when a conductor to be connected is forced into said slot said conductive means form respective beams clasping said conductor and applying pressure thereto, a layer of indium coating said conductive means at said slots, and insulating means for supporting said conductive means and for surrounding said conductive means after connection to a wire.

2. A connector as in claim 1 wherein said conductive means comprise a C-shaped unit terminating at the ends in two pairs of slotted posts.

3. A connector as in claim 1 wherein said frame means include means for embracing said wires to be connected and holding them parallel to each other and means for olfsetting the wires as they emerge from their parallel positions.

4. A connector for interconnecting the conductors of a pair of insulated wires, comprising rigid metallic conductive means forming a plurality of slots, insulating means supporting said conductive means, frame means for receiving a pair of wires, said frame means having projections for offsetting said wires when they are placed in said frame means, said frame means being engageable with said insulating means and being engaged therewith when a connection is made, said frame means defining a plurality of recesses for receiving said conductive means when said frame means engages said insulating means, said recesses being aligned so that when said frame means and said insulating means are made to engage each other said frame means force the conductors of the wires to be connected into the slots formed by said conductive means.

5. A connector as in claim 4 wherein said conductive means comprise a C-shaped unit terminating at each arm in a pair of slotted posts.

6. A connector as in claim 5 wherein said insulating means include a box-like trough in which the common member of said C-shaped unit is bonded so that said posts project upwardly toward the opening of said trough, frame means for holding wires to be connected parallel to each other engageable with said trough at the open end of said trough and forming a snap fitting therewith when fitted therein, said frame means defining a plurality of recesses for receiving the posts, said frame means when being engaged with said trough forcing the wires to be connected into said slots whereby said slots tear away the insulation and clasp the conductors of said wires.

7. A connector as in claim 6 wherein said trough includes a pair of ears extending therefrom for embracing said projections.

8. A connector as in claim 7 wherein upstanding damming walls project astride said C-shaped unit for enclosing said encapsulating material within the area of said unit and wherein said frame means include additional recesses for receiving said damming walls, said damming walls including a plurality of slits aligned with the slots of said unit for grasping the insulation on the wires to be connected when said wires are forced into said slots.

9. A connector as in claim 4 wherein said insulating means form a trough-like case surrounding said conductive means and said conductive means are bonded to said insulating means.

10. A connector as in claim 9 wherein said insulating means include a pair of damming walls, and encapsulating means between said damming walls, said damming walls forming slits aligned with said slots for holding the wires as they emerge from the slots.

References Cited UNITED STATES PATENTS 2/ 1951 Netherlands.

DARRELL P. CLAY, Primary Examiner US. Cl. X.R.

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