CONNECTOR FOR CONNECTING A PLURALITY OF INDIVIDUAL INSULATED WIRES WITH ELECTRICAL CONTACT ELEMENTS

Field of the Invention

The invention refers to a connector for connecting a plurality of individual insulated wires with electrical contact elements, particularly of a flat cable having closely spaced wires.

Background of the Invention

Above all, in the microelectronics there is a growing tendency to miniaturization and the continued necessity of reliably connecting a plurality of closely spaced wires or conductors with electrical contacts. The wires for example are individual discrete wires or are arranged in a flat cable. Usually, the contact elements have a pin or a receptacle at one end arranged in two or more rows on a retaining body adapted to receive pins of a matched plug device. The distances between the receptacles or the plug pins, respectively, are standardized.

It is known to establish an electrical connection with a plurality of wires by a plurality of U- shaped insulation displacing contact elements which engage the wires concurrently. In order to accomplish that the contact elements are accurately oriented with respect to the associated wires, it is known to press the wires by a pressing body against the contact elements of the retaining body. The pressing body includes recesses or pockets into which the free ends of the cutting contact elements are plunged. It is further known to provide grooves or passages in the pressing body wherein the wires are guided across the width of the pressing body to locate the wires with respect to the contact elements. In order to connect a maximum number of closely spaced wires having a small diameter with a connector, it is suggested by the German patent

closely spaced wires having a small diameter with a connector, it is suggested by the German patent specification 39 20 367.0 to provide relatively short groove-like guiding sections adjacent the recesses extending only along a portion of the width of the pressing body whereby the wires are permitted to yield laterally beyond the guiding sections. Beyond the guiding portions, the wires may move laterally a certain amount and may yield laterally if retaining body and pressing body are pressed against each other. By this, two or more rows of cutting contact elements can be brought into engagement with a plurality of contiguous wires having a small diameter. Care is taken in the area where the contact elements cut into the insulation of the associated wire that the wire is exactly aligned with the contact element.

It is known from the German specification 29 41 029 to establish an electrical contact with a wire by three prongs, a first and a second prong being located at a distance from each other while a third prong is located in the gap between the first and second prong and forms a slot with the first and second prong for the accommodation of a wire. The edges of the prongs facing the slot are chamfered. With the known contact elements, it is intended to achieve smaller outer dimensions for the connector. However, the dimensions of the connector in the direction of the wires are relatively large which above all are of some effect when more than one row of contact elements is required. Finally, a U-shaped insulation displacing contact elements are known arranged in two or more parallel rows which define a receiving slot for a wire by two approximately parallel legs, the width of the slots being smaller than the diameter of the wire, and the legs having a smaller first portion of approximately constant width adjacent the free end

thereof and a broader second portion joining the first portion and having also a constant width. With the aid of such contact elements, a flat cable with an extremely small pitch can be connected to a connector without the insulation of the wires adjacent to the contact elements being damaged. Owing to the configuration of the second leg portions, the available predetermined contact force is relatively small so that it may occur that after a longer time of operation, the necessary contact force cannot be generated if the wire yields a certain amount. The shape of the second leg portions further causes a relatively high stress in the area of the connection to the web so that a permanent deformation may occur whereby the desired contact force cannot be maintained. The selected shape of the legs of the known contact elements further requires a relatively great length for the legs to ensure that the contact force is not too high. Thus, the stress in the leg portion adjacent to the web is particularly high.

The present invention provides connector means for connecting a plurality of insulated wires with electrical contact, particularly of a flat cable having closely spaced wires which allows a connection also with extremely small pitches which further makes available a predetermined contact force for a longer time period and which avoids stress peaks in the contact elements.

Summary of the Invention

With the connector means according to the invention, the second leg portions of the U-shaped contact elements broaden gradually away from the first leg portions such that the bending load on the second leg portions upon receipt of a wire between the contact legs is approximately constant about its length.

According to an embodiment of the invention, the outer edges of the second portion are straight and have a shape extending obliquely outwardly. According to a further embodiment of the invention, the transition area of the first and second leg portion is located in a plane including the axes of the wires.

According to another embodiment of the invention, the pitch of a row of contact elements is twice of the pitch of the wires, and the sizes of the second portion of the contact legs are such that the outer edge of the second portion engages or slightly deforms the insulation of the adjacent wire. With such a design, a connection with flat cables can be achieved having a small pitch of 0,635 mm.

Beyond the area of the contact elements, the wires are preferably retained in guiding means of the retaining body and the pressing body, respectively. According to a further embodiment of the invention, the legs have obliquely extending edge portions at the free ends thereof to define a gradually narrowing entrance portion for the wire. By this, that the wire is accurately positioned in the slot between the legs of the contact elements if retaining body and pressing body are pressed against each other. Outer chamfers of the legs of the contact elements serve for a similar purpose, i.e. effect that adjacent wires are laterally deflected so that the wires are accurately located between the legs of adjacent contact elements.

The force by which the wire is pressed between the legs of U-shaped contact elements is predetermined. It is to be maintained about a longer time period in order to restrict the electrical contact properties being reduced after a certain time of operation by an increase

of the transition resistance. With a small pitch of the wires, the width of the first portion of the legs is relatively small. Also the width of the second portion is limited if a relative small pitch of a row of contact elements is intended, e.g. a pitch which is twice the small pitch of the wires. In contrast to conventional U- shaped contact elements, the necessary contact force can for example be achieved in that the length of the legs is made shorter. If for example the length of the legs of conventional contact elements used for a wire pitch of

1,27 mm is 2 mm, the length of the legs in the invention is shortened for example to 1,4 mm. The shortening of the legs to achieve the necessary contact force, however, is uncritical if the legs are formed according to the teaching of the invention. The design of the legs according to the invention effects a uniform distribution of the stress and, thus, provides an optimum utilization of the material in view of its resiliency. Peak stresses which for example can lead to a permanent deformation at the joint between the legs and the web do not occur.

The design of the legs according to the invention allows a double deflection with the same spring force in comparison with conventional contact elements. This means that the legs can be deflected a greater amount without causing a permanent deformation. Furthermore, the legs can yield a greater amount if they dig into the wire or if the wire attains a smaller width due to a later deformation, or if the wire moves slightly outwards of the slot between the legs without the contact force being reduced considerably.

Summarizing, it can be stated that the shape of the contact elements according to the invention allows an optimum utilization of the material and, thus, allows an extensive contact miniaturization with a predetermined

contact force. Furthermore, the contact force is applied through a larger deflection range and, therefore, remains sufficiently high also after a longer time of operation to maintain a reliable electrical contact.

Brief Description of the Drawing

The invention will be subsequently described by means of an embodiment example in connection with the accompanying drawing.

The single Figure is a cross section through a portion of the connector means according to the invention.

Detailed Description of the Presently Preferred Invention

In the Figure, a retaining body 10 is indicated which may be comprised of plastic material. The retaining body can have a configuration as described in connection with the German patent specification 39 20 367.0. It may include plug means (not shown). The retaining body 10 for example includes two rows of resilient receptacles to receive pins of a plug arrangement (not shown) . Each receptacle is associated with a U-shaped contact element 12. Three contact elements 12 of a row of contact elements can be seen in the drawing, the retaining body 10 receiving two rows of contact elements correspondingly positioned but offset by the pitch of the contacts.

A pressing body 20 of plastic material has a similar configuration as retaining body 10. According to the already mentioned German patent specification 39 20 367.0, it can be provided with recesses for the receipt of the contact means of retaining body 10.

A flat cable 30 consists of a plurality of closely spaced wires having a conductor 34 and an insulation 36. The insulations 36 are interconnected through webs (cannot be seen in drawing) as is well known in the art.

The support surface of the retaining body 10 is indicated by the dash-dotted line 14. In the area of the row of contact elements 12, a throughgoing slot is formed in retaining body 10 the deeper portion which is indicated by line 18 and enlarging conically in cross section towards support surface 14. Individual stepped slots 40 for the receipt of contact elements 12 are open to throughgoing slot 16. They are formed such that they correspond to the outer contour of contact elements 12. Beyond slot 16, the support surface 14 has guide means for the wires 32 of the cable (as known per se) .

The pressing body 20 has recesses 22 for the receipt of contact elements 12. The webs between recesses 22 are rounded at 24 at the free ends for the guidance of the wires 32 of flat cable 30 also in the area of the recesses.

In the following, the design of the contact elements 12 is to be described in connection with the central contact element in the drawing. The contact elements 12 are made of electrically conductive metallic sheet material and are for example cut out of the sheet material. The contact elements 12 include two legs 42,

44. The legs 42, 44 include a first portion 46, 48 and a second portion 50, 52. The legs 42, 44 define a slot 54 having parallel walls and a rounded bottom. The width of slot 54 is smaller than the diameter of conductor 34. The first portions 46, 48 have substantially a constant width throughout their length. The first portions 46, 48

are provided with an obliquely extending edge 56 for the formation of a gradually narrowing entrance portion of slot 54. The portions 46, 48 also include laterally facing chamfers 58 at the free end thereof.

The second portions 50, 52 gradually broaden away from first portion 46, 48 such that the bending stress of the second portion is substantially constant throughout its length upon receipt of a wire between legs 42, 44. The legs 42, 44 are connected to a portion 60, a subportion 62 thereof adjacent to the end of slot 54 having a width which is slightly larger than the width of slot 40. Below subportion 62, the portion 60 has a width corresponding to that of receiving slot 40. The width of portion 60 reduces downward stepwisely with a portion 64 being connected to a receptacle (not shown) .

In a practical embodiment, the pitch of the cables 32 is 0,635 mm. The legs 42, 44 have a length of 1,4 mm and extend beyond support surface 14 of retaining body 10 about 1,0 mm.

Upon a connection of wires 32 of flat cable 30 with the contact elements 12, the flat cable 30 is positioned between retaining body 10 and pressing body 20. Thereafter, pressing body 20 and retaining body 10 are pressed against each other. The wires 32 are guided and retained in their position beyond the contact elements 12; the contact elements 12 engage the conductors 34 in that the portions 46, 48 first pierce through the insulation 36 and gradually get in contact with the conductor 34. The portions 46, 48 are slightly deflected outwardly exerting only a relatively small spring force. When the conductor 34 approaches portions 50, 52, the spring force increases depending upon the configuration of portions 50, 52. Certainly, the spring

force also depends upon the length of slot 54. The longer the portions 50, 52 are, the less is the attainable clamping force. The clamping force to generate a predetermined contact force on conductor 34, is predetermined. On the other hand, the maximum width of the second portions 50, 52 is limited through the mentioned pitch of flat cable 30. The length of portions 50, 52 therefore has to be selected such that with a predetermined thickness of portions 50, 52, the necessary contact force can be achieved. The shape of portions 50, 52 avoids peak stresses in that the load on portions 50, 52 throughout the length is substantially constant. Furthermore, the shape of portions 50, 52 allows a relatively large deflection with a constant contact force and, thus, satisfactorily establishing the electrical contact independent of whether the diameter of the conductors 34 is subject to tolerances or whether the conductor is deformed by the engagement of legs 42, 44.

As can be seen, legs 42, 44 of adjacent contact elements 12 leave sufficient space for the accommodation of wire 32 with the insulation 36 thereof being deformed only to a minor extent. Such a deformation can be accepted since the electrical properties of wire 32 are not affected. The outer chamfers 58 on legs 42, 44 effect that the wires 32 between adjacent contact elements 12 can attain the shown position and are not unilaterally stressed by the outer edge of a leg 42 or 44, respectively, in order to avoid a leg piercing into the insulation 36 or engaging conductor 34.