WO2015049470A2

WO2015049470A2 - Method for producing an electrical contact, and electrical contact

Info

Publication number: WO2015049470A2
Application number: PCT/FR2014/052503
Authority: WO
Inventors: Ning Yu
Original assignee: Axon Cable
Priority date: 2013-10-04
Filing date: 2014-10-02
Publication date: 2015-04-09
Also published as: CN105594068B; WO2015049470A3; EP3053223A2; FR3011691B1; EP3109948A1; CN105594068A; FR3011691A1; EP3109948B1

Abstract

A method for producing an electrical contact (100) which involves: b) producing a tube (30) by forming the edge of a strip; e) without detaching the tube (30) from the strip (12), securing a first conductive element (20) in a first end (31) of the tube, such that a portion of the tube remains empty at the second end (37) of same. An electrical contact comprising a tube (30), and a contact terminal (20) of which one end is secured in a first end (31) of the tube (30); and in which inner surface (32) of the tube is covered with a surface coating (16, 18) called the inner coating, and the thickness of the inner coating, or at least of one layer of the inner coating, is at least equal to 1 μm, or indeed 1.27 μm.

Description

Method of manufacturing electrical contact, and electrical contact

The invention relates to a method for manufacturing electrical contacts.

By "electrical contact" is meant here a part or a set of parts, adapted to be attached to one end of a conductive element, to ensure electrical contact between the conductive element and another conductive element. This 'other conductive element' is generally also an electrical contact.

The female contact may simply be in the form of a tube.

The male contact is generally constituted essentially by a contact terminal (conductive part, male or female), and a conductive junction piece (more simply called 'the junction') on which is mechanically and electrically fixed the terminal, the junction being arranged in addition so as to be mechanically and electrically fixed to a conductive element.

The expression "conductive element" is broadly intended to cover any body of which at least part is electrically conductive; it may include an electrical wire, or a contact terminal.

The term "terminal" or "contact terminal" herein refers to a part (or portion of a part) intended to reversibly contact another part (another terminal) so as to make an electrical contact; it is not a part for the permanent fixing of an electric wire, for example by crimping.

The manufacture of electrical contacts is a preliminary operation performed when attaching connectors to the end of electrical cables, including data transmission cables.

Indeed, to fix a connector at the end of a cable, contacts are prepared at the end of each of the electrical son making up the cable, and then the contacts are fixed to the connector. The connector then allows the connection of the cable to one or more other devices.

The invention particularly relates to the manufacture of electrical contacts for connecting electronic systems in a particularly compact manner, using a minimum volume.

Different standards have been developed to define electronic system connectors. Among these, Mil-DTL-32139 standards or Mil-DTL-83513 defines male and female rectangular connector families that allow particularly compact connections:

The Mil-DTL-83513 standard defines so-called "micro-D" connections, characterized by a spacing of 1.27 mm between adjacent conductors; and the Mil-DTL-32139 standard defines so-called "nano-D" connections, characterized by a 0.635 mm spacing between adjacent conductors.

The invention therefore relates in particular to the manufacture of contacts designed to be integrated in connectors complying with one or the other of these standards, or at least designed to be spaced apart with centers of the order of 0.635 mm or 1.27 mm.

Various techniques are known for making electrical contacts. The technologies known as "flexpin" and "twist-pin" are particularly known.

Flex-pin technology

In this technology, the manufacture of a contact is made from a copper alloy strip by a technique called "cut and rolled", hereinafter called cutting. This technology is for example illustrated by the patent US 4,820,207.

With the help of an automatic machine equipped with a tool of great precision, is made on the edge of the strip a cut adapted to make the contact.

To make a female contact, the cut is formed so as to give it the shape of a tube.

To make a male contact, the cut is formed so as to give it the shape of a tube extended by an electrical terminal.

The shape of electrical terminal chosen is of the type comprising a radially elastic bulge, serving to ensure the mechanical retention and electrical continuity when mating with the female contact.

After forming the contact, it is covered by a surface coating (usually a nickel undercoat followed by a gold layer) by electrolysis.

Due to the low cost of the strip used and the efficiency of the cutting process, the cost of manufacturing electrical contacts by Flex-pin technology is relatively low.

However, if the inside diameter of the tube that the contact comprises becomes weak (as for example, to correspond to the Nano-D type, a diameter of 0.25 mm to 0.35 mm) the realization of surface coatings inside the tube becomes impossible, the inner surface of the tubes receiving virtually no coating during electrolysis.

It is therefore not possible to improve the physicochemical properties of the tube by means of surface coatings.

As a result, this technology is limited to contacts whose tubes are of relatively large diameter.

Twist-pin technology

In this technology, the manufacture of a female contact is simply to produce a tube, by high-precision machining.

The manufacture of a male contact, in turn, comprises three steps: a first conductive element is first made which is an electrical terminal consisting of a strand comprising one or more central strands and peripheral strands, and having a bulge ( called "bump") in the central part; a tube is manufactured by a high-precision machining operation identical to the manufacture of the female contact; the strand is fixed in one end of the tube.

This technology is for example illustrated by the US Pat. No. 4,358,180. In the traditional way in electrical connection, the contact terminals are made of copper or copper alloy, coated with a nickel undercoat and a gold coating.

However in contrast, according to the technology 'twist-pin', the strand constituting the electrical terminal of the male contact is made of precious metals: The different strands are made of precious alloy.

The particular shape of the strand with its various strands forming a bulge, and their specific chemical composition indicated above, allow such a strand to constitute a contact terminal having very high performance in terms of connection, especially in harsh environments.

On the other hand, as for the twist-pin technology, the realization of a coating by electrolytic deposition on the inner surface of the tube is difficult, if not impracticable, when the diameter of the contact tube becomes very small.

In twist-pin technology, this difficulty is overcome by realizing the tube itself in 18-carat gold (or in Au-Ag alloy, or Au-Ag-Cu). As a result, given the materials used, the contacts made by Twist-pin technology are relatively expensive.

Also, a first object of the invention is to propose a method for manufacturing electrical contacts making it possible to produce electrical contacts at a reasonable cost, in particular comprising a small diameter tube, the internal surface of which has high physicochemical performances, guaranteeing a high high operating time.

This objective is obtained by means of a first electrical contact manufacturing method, comprising the following steps:

a2) is provided a strip having, on at least a portion of one of its faces, and along one of its edges, a first surface coating; then

b) forming a tube forming the edge of the strip, the tube being formed so that the coating is inside the tube.

For the implementation of the method, it is of course possible to use a strip on which the first surface coating has been deposited in advance.

However, it is also possible to deposit said first surface coating at least on said portion of the face of the strip and along said edge of the strip during a first step al) of the method.

The first surface coating can be any coating improving a property of the tube, including corrosion resistance. The first surface coating may be in particular a gold-based coating, preferably with a nickel-based underlayer.

The first surface coating must be deposited at least on a portion of the strip that will be brought to be inside the tube. Nothing prevents the first surface coating on a larger portion of the strip, for example over the entire face of the strip, or on both sides of the strip.

The strip used may in particular be packaged in a reel.

In the contact, the tube acts as an electrical joining piece; its shape allows it in a simple way to provide the connection between two conductive elements, including an electrical wire and a contact terminal. Advantageously, the tubular shape is an easy form to make from a strip, especially by known cutting and forming operations. Preferably, the tube formed in step b) is left integral with the remainder of the strip, that is to say fixed on it: This thus makes it possible to maintain the different tubes at a predetermined constant distance from each other , which then makes it possible to automate the subsequent manufacturing steps.

As indicated above, the surface coating is applied on the face of the strip which will be, after step b) of forming the tube, inside the tube. Thus, unlike prior twist-pin technology in which the surface coating was applied after the manufacture of the tube, in this first method according to the invention the surface coating is applied before the manufacture of the tube.

As a result, the thickness and the different properties of the coating are controlled, which ensures the quality of the coating produced. In particular, it is possible to use not only electrolysis, as a coating method, but also other coating processes, such as rolling.

Advantageously, this first method indicated above makes it possible to produce the tube with materials whose cost is much lower than those used in twist-pin technology. Thus, for example, the tubes may be made of a copper alloy coated with nickel and gold.

In addition, the diameter of the tube can be extremely small, without this posing problems of application of the surface coating on the inner face of the tube, in contrast to prior contact manufacturing processes.

When the tube is left attached to the strip, the first method can be implemented continuously, and more specifically in "real to real", that is to say from coil to coil. Thus at the end of manufacture, the contacts, male and female, are attached to the strip of strip and arranged regularly thereon with a constant pitch. The fact that the contacts remain fixed on the strip is an important advantage since it makes it possible to automate the connection operation of the contacts relatively easily.

Thus, thanks to the low price of the strip used and the efficiency of the cutting process, the cost of manufacturing tubes for electrical contacts by this first method is much lower than by Twist-pin technology.

The embodiment of the tube on the edge of a strip provides a second advantage. The first method according to the invention presented above can of course be used to make female contacts, which simply consist of tubes.

This first method can also be implemented to make male contacts in the context of Flex-pin technology: the terminal is then formed integrally with the tube.

However, the method according to the invention can also be implemented differently, in particular to make male contacts.

Indeed, in terms of functional reliability the male and female contacts obtained by the Flex-pin technology are much less efficient than those made by Twist-pin technology, especially when used in severe environments such as vibration, heat, humidity, etc. Indeed, the terminals by cutting and forming of copper-based alloy strip are much less efficient than the strands based on precious materials used in the twist-pin process.

A second object of the invention is to remedy this problem by proposing a method of manufacturing electrical contacts for making electrical contacts that can be inexpensively integrated in electrical connectors and having high qualities in terms of mechanical strength, and electrical conductivity, especially in harsh environments (vibration, heat, humidity, ...).

This objective is obtained by means of a second aspect of the process, or more generally of a second method, comprising the following steps:

b) forming a tube forming an edge of a strip;

e) without detaching the tube from the strip, a first conductive element (in particular a contact terminal) is fixed in a first end of the tube, so that a portion of the tube remains empty on the side of the second end thereof. .

This method can be implemented independently of the possible presence of surface coating (s) applied (s) or previously applied (s) on the strip.

However, preferably the strip whose edge is formed in step b) has, on at least a portion of one of its faces and along said edge of the strip, a first surface coating. For this purpose, the method may in particular comprise a step a) in which, at least on said part of the face of the strip and along said edge of the strip, depositing said first surface coating.

The method is also intended to be implemented iteratively, during the continuous unwinding of the strip (It is the same for the various possible additional steps of the process, described below).

For this purpose, the strip used is preferably packaged in a coil.

In this second method, the contact terminal or more generally the first conductive element is made separately from the tube, and then fixed inside the first end thereof. As a result, a first element having the desired performance in terms of mechanical strength and electrical conductivity can be selected, particularly in harsh environments.

In this second method, it is important that the second end of the tube remains free and accessible for a distance sufficient to allow the attachment of another conductive element inside, in particular by welding or crimping. Preferably, the remaining empty tube portion has a length of at least 1 mm.

This second method (as also the first) is preferably implemented to mass-produce series of contacts; the tubes made are then generally parallel. The spacing separating adjacent tubes is normally defined according to the standard to be met by the contacts made. For example to make nanoD type connectors, the contacts must be spaced 0.635 mm; to make micro-D connectors, they must be spaced 1.27 mm apart.

To facilitate the winding of the strip on a coil at the end of the process (the strip then supports the different contacts), the tube is preferably formed such that its axis extends in the (local) plane of the strip. The axis may in particular be perpendicular to the general direction of the strip. The tube may however be oriented differently, for example so that its axis is perpendicular to the plane of the strip.

Advantageously, the manufacture of contacts by this second method is inexpensive, because all operations can be performed in 'reel to reel' mode ("real to real"). This type of manufacturing allows a high processing rate by reducing the handling of parts. In particular, the continuous forming and cutting of the strip with the following tools makes the production of tubes much more economical and faster than the precision turning required by Twist-pin technology.

In addition, since the contacts obtained remain fixed on the strip of strip, they can be packaged on a coil. It is therefore possible to automate the operation of fixing the contacts in electrical connectors. This last operation can be done at a much lower cost than if the contacts were obtained in bulk.

The first and second methods presented above can be implemented jointly, so as to make male electrical contacts comprising on the one hand a tube whose inner surface has high physico-chemical performance, and also having high qualities in terms of mechanical resistance, electrical conductivity, etc.

According to particular embodiments of the invention, the methods for producing contacts according to the invention presented above may comprise one or more of the following characteristics, taken separately or in technically possible combinations:

The tube may be, but not necessarily, of circular section.

- The first surface coating can be applied by electrolysis or by hot rolling.

- The method may further comprise a step d) in which is deposited on an outer surface of the tube a second surface coating. This surface coating provides protection for the surfaces of the tube other than its inner surface, namely its outer surface, as well as the slices of the tube (surfaces connecting the inner surface to the outer surface of the tube). The second surface coating can be applied by electrolysis.

The first and second surface coatings can in particular be anticorrosive coatings. The first and / or second surface coating may thus comprise a nickel sub-layer coated with a gold layer.

The method may further comprise a step c) in which the edges of the tube are welded to obtain a seamless tube. Indeed, if the edges facing the tube are not fixed to each other, the tube may deform either during the subsequent steps of the method, in particular the crimping steps, or during the operation of the contact. The welding of the edges of the tube makes it possible to eliminate this risk of deformations. This welding can be made in particular by laser. The edges of the tube that are welded to each other are only the two contiguous edges of the tube, placed opposite one another in step b), when the tube is formed from the strip.

In addition, the method may comprise in particular the following characteristics:

- In step e), the fixing of the first conductive element can be made by crimping, in particular by an axisymmetric crimping operation. Such an operation, in particular in the case of a tube of circular section, allows it to maintain a minimum diameter, and in particular avoids the ovality of the tube. The crimping can for example be done with 3 or 4 axisymmetric imprints. Alternatively, in one embodiment, the fixing of conductive elements in the tube (whether contact terminals or electrical son) can be made by force insertion or by welding or solder.

- The method may further comprise a step f) wherein, the tube remaining attached to the strip, is fixed one end of a second conductive member in the second end of the tube. At the end of the process, the contact is then obtained directly attached to the end of the second conductive element. Fixing the second conductive element to the tube can be done in particular by crimping, after inserting the end of the second conductive element in the tube. The second conductive element may in particular be an electrical wire.

The first conductive element may typically be an electrical contact terminal, male or female.

- The first conductive element may in particular be a strand. A strand is an electrical component consisting mainly of a set of strands twisted together. The first conductive element may thus be for example a strand comprising a central core with one to three strands, and a plurality of peripheral strands.

Another object of the invention is to propose an electrical contact of small dimensions, in particular radial, allowing the integration thereof into connectors requiring a small center distance, of the order of 1 mm, for example equal to 1.27 mm or 0.635 mm; and showing performance high in terms of resistance to stress, especially temperature, mechanical, etc.

This objective is achieved through an electrical contact comprising a tube, and a contact terminal whose end is fixed in a first end of the tube; wherein an inner surface of the tube is covered by a surface coating said inner liner; and wherein the thickness of the inner liner, or at least one layer of the inner liner, is at least 1 m, or even 1.27 μm.

Preferably, if the inner coating comprises several layers, the thickness of at least one layer, or even each of these layers, is at least equal to 1 μm, or even 1.27 μm.

Preferably in this contact (and this is also applicable if the inner lining has a thickness less than 1 μm), if furthermore the outer surface of the tube is covered by a surface coating, said outer coating, the thickness of the inner liner is at least equal to the thickness of the outer coating.

A contact as presented above may in particular be manufactured by the first or the second method indicated above. It may exhibit the different characteristics conferred by the processes presented above, and / or the following characteristics, taken separately or in combination:

The internal coating may comprise at least two layers, which are substantially of the same chemical composition as layers of the outer coating.

- The tube can be a seamless tube

- The electrical contact may further comprise, in addition to the contact terminal, a second conductive element fixed in the second end of the tube.

This second conductive element may be an electrical wire.

- The electrical contact terminal can be male or possibly female. It may in particular be a strand, in particular a strand having a central core with one to three strands, and a plurality of peripheral strands.

The invention will be better understood and its advantages will appear better on reading the following detailed description of embodiments. represented as non-limiting examples. The description refers to the accompanying drawings, in which:

FIG. 1 schematically represents a mode of implementation of the method according to the invention; and

FIG. 2 is a sectional view of the tube of one of the contacts manufactured using the method presented in FIG.

The method according to the invention is presented in an embodiment which combines the first and second methods presented above.

For the implementation of this method, the following components are first provided:

- A coil 10, on which is wound a strip 12 of copper alloy strip;

- Male contact terminals 20. These are constituted in a manner known per se from a twisted rope of seven strands of cuprous alloy

(one strand in the center and six strands on the periphery). The different strands of the strand are welded together at each of the two ends of the strand. The strand has on its central part a bulge (or "bump"), which allows the fixing of the terminal inside a corresponding female terminal.

- Electrical son 50. Each wire 50 comprises a conductive core 52 and an electrical insulating coating 54, including fluorinated ethylene-propylene copolymers (FEP).

The actual manufacturing process then comprises the following successive steps, represented in a synthetic manner in FIG.

To form a male contact 100, the following operations are successively carried out:

al) is deposited on a portion 14 of the strip 12 a nickel underlayer 16.

a2) is deposited on a portion of the strip a gold layer 18.

bl) cut the edge of the strip.

b2) a tube 30 is formed with the coated strip so that the coated portion 14 forms the inner surface 32 of the tube, the latter having two contiguous edges 34,35.

c) the two contiguous edges 34,35 of the tube 30 are welded using a laser.

dl) electrolytically depositing a nickel underlayer 36, at least on the outer surface 40 and on the slices 42 of the tube 30. d2) electrolytically depositing a gold layer 38, also at least on the outer surface 40 and on the slices 42 of the tube 30.

el) inserting a male terminal 20 in a first end 31 of the tube obtained in step d).

e2) the male terminal 20 is crimped into the tube 30 by crimping at four symmetrical points (manual or automatic).

fl) one end of the electrical wire 50 is stripped with a laser source. f2) the stripped end of the electrical wire 50 is inserted into the second end 37 of the tube 30.

f3) is crimped the end of the wire 30 inserted into the second end 37 of the tube 30 by crimping at four axisymmetric points.

Steps a1 and a2 correspond to step a) indicated above, steps b1 and b2 correspond to step b) indicated above, etc.

In FIG. 1, the machines and equipment necessary for carrying out the different steps of the process are not represented.

At the end of the process, we obtain a set of male contacts 100, mounted at the end of electrical son and thus ready to be mounted in a nano-D or micro-D connector. Each male contact 100 secures a male terminal 20 in the form of a strand to one of the electrical wires 50.

Since the contacts 100 are packaged on the strip strip 12, their insertion and attachment in electrical connectors can be automated in a relatively simple manner.

The method thus makes it possible to obtain contacts in particular of the micro-D or nano-D type, male and female. The manufacturing method of the female contacts is identical to that of the male contacts, except that the step e) of fixing the contact terminal (or first conductive element) 20 in the tube 30 must not be carried out. The first end 31 of the tube thus remains empty and thus ready to receive a male contact terminal.

Preferably, at least steps a) to d), and preferably all steps are performed without detaching the tube from the strip. The manufacturing process is thus a continuous process (real to real). In particular, the steps b1) for cutting and b2) for forming the tube are carried out continuously. The strip of strip 12 is thus unrolled continuously from the coil 10, before being wound on a coil 60. The contacts 100 obtained at the end of the The method, attached to the strip of strip 12, is thus wound on the coil 60.

In step b1), the edge of the strip is cut to form a rectangular cut, connected to the rest of the strip by a narrow tab. The dimensions of the cutout are provided so that the cut can be bent to form the tube 30, in step b2).

The surface coatings 16 and 18 made in steps a1) and a2) constitute the first surface coating within the meaning of the invention. These coatings can be applied electrolytically or by hot rolling.

The thickness of the surface coating 16 as well as the thickness of the surface coating 18 are each at least 1 μm. In fact in the present case, each of these coating layers has a thickness of at least 1.27 μm.

The surface coatings 36 and 38 made in steps d1) and d2) constitute the second surface coating within the meaning of the invention.

In general, the second surface coating, made in step d), is also partially deposited on the inner surface of the tube. As a result, the coating thickness Ti on the inner surface 32 of the tube 30 is usually greater than the coating thickness Te on the outer surface 40 of the tube (Fig.2).

Steps d1 and d2 are preferably carried out only on the tubes, to limit the consumption of nickel and gold. For this purpose, the strip of strip 12 is oriented such that in steps d1) and d2), the tubes 30 are placed on the bottom side of the strip strip.

In step b2), when the contacts 100 manufactured must respect the nano-D type, the tubes are formed with an inside diameter of between 0.25 and 0.35 mm.

Strips having different compositions can be used for the manufacture of the contacts 100. For example, a C17200 ternary alloy strip, namely Cu98.0-Bel, 8-Co0.2; ternary alloy C31400, namely Cu90-Zn9.5-Ni0.5; or else quaternary alloy C17510, namely Cu-97.8-Nil, 9-Be0.3.

The strip 12 of copper alloy strip may have a width of between 20 and 30 mm, and a thickness of between 0.06 mm and 0.09 mm. The surface coatings applied in steps a) and d) are generally of the same chemical composition. These are generally anticorrosive coatings, in this case composed of a nickel undercoat, coated with a gold layer.

In step a), the coating may be applied to the edge of the strip over a width of 1.5 to 4 mm, for example over 2.25 mm.

The nickel-based coating sub-layer deposited in step a1) or in step d1) can have a minimum thickness of 1.27 μιτι. This thickness is usually chosen between 1 and 10 μηη.

The gold-based coating layer deposited in step a2) or in step d2) may have a minimum thickness of 1.27 μm. This thickness is usually chosen between 1 and 10 μm. For example, the nickel underlayer may have a thickness of 0.005 mm, and the gold layer a thickness of 0.005 mm.

The nickel-based coating sub-layer deposited in step a1) or in step d1), and / or the gold-based coating layer deposited in step a2) or in step d2 ) can be performed by a hot rolling operation followed by a heat treatment operation.

The tubes formed in step b) may have a length of 1.5 to 4 mm, an inside diameter of 0.2 to 0.6 mm, and an outside diameter of 0.35 to 1 mm. For example, the contacts 100 can be made with tubes of length 2 mm, or 3.15 mm.

The contacts 100 may also be made with tubes whose internal diameter is 0.33 mm, and the outer diameter of 0.46 mm. They can still be made with tubes whose inner diameter is 0.54 mm.

Although in the embodiment of the invention presented as an illustrative example, the method serves to manufacture a contact comprising, as first conductive element, a contact terminal, the method can be implemented with any other conductive element as the 'first conductive element', for example an electrical wire.

Similarly, although in the embodiment of the invention presented by way of illustrative example, the contact 100 comprises a male contact terminal 20, the contact may also comprise as a first conductive element a female contact terminal.

Claims

A method of manufacturing an electrical contact (100), comprising the steps of:

b) forming a tube (30) forming an edge of a strip;

the process being characterized in that it further comprises a step e) in which:

e) without detaching the tube (30) from the strip (12), a first conducting element (20) is fixed in a first end (31) of the tube, so that a portion of the tube remains empty on the side of the second end (37) thereof.

2. The method of claim 1, wherein the strip (12) whose edge is formed in step b) has, on at least a portion of one of its faces and along said edge of the strip, a first coating surface (16,18).

The method of claim 2, further comprising a step a) wherein, at least on said portion of the face of the strip (12) and along said strip edge, said first surface coating is deposited (16, 18 ).

4. The method of claim 2 or 3, wherein the first surface coating (16,18) is applied by electrolysis or hot rolling.

The method of any one of claims 1 to 4, further comprising a step d) wherein a second surface coating (36,38) is deposited on an outer surface (40) of the tube.

6. A method according to any one of claims 1 to 5, further comprising a step c) in which the edges (34, 35) of the tube are welded to obtain a seamless tube.

7. Method according to any one of claims 1 to 6, wherein in step e), the fixing of the first conductive element (20) is made by crimping, in particular by an axisymmetric crimping operation.

The method of any one of claims 1 to 7, further comprising a step f) wherein, the tube (30) remaining attached to the strap (12), one end of a second conductive element (50) is fixed in the second end (37) of the tube (30).

The method of claim 8, wherein the second conductive member is an electrical wire (50).

The method of any one of claims 1 to 9, wherein the first conductive member is an electrical contact terminal, male or female.

The method of claim 10, wherein the first conductive member is a strand, including a strand having a central core with one to three strands, and a plurality of peripheral strands.

12. Electrical contact (100) comprising a tube (30), and a contact terminal (20), one end of which is fixed in a first end (31) of the tube (30); the contact being characterized in that an inner surface (32) of the tube is covered by a surface coating (16, 18), said inner liner, and that the thickness of the inner liner, or at least one layer of the liner internal, is at least equal to 1 μηη, or even 1.27 pm.

The contact of claim 12, wherein further, an outer surface (40) of the tube is covered by a surface coating (36,38) said outer coating; and a thickness (T,) of the inner liner is at least equal to a thickness (T _e ) of the outer liner.

14. Contact according to claim 12 or 13, the tube is a seamless tube.