WO2010076486A1

WO2010076486A1 - Method for manufacturing a connector element including a substrate on which a layer of gold is deposited

Info

Publication number: WO2010076486A1
Application number: PCT/FR2009/052545
Authority: WO
Inventors: Denis Busardo
Original assignee: Quertech Ingenierie
Priority date: 2008-12-16
Filing date: 2009-12-15
Publication date: 2010-07-08
Also published as: FR2939973A1; FR2939973B1

Abstract

The invention relates to a method for manufacturing a connector element including a substrate on which a layer of gold is deposited, which includes the following consecutive steps: a) providing a substrate (20); b) treating a surface of the substrate (20) by ion bombardment using an ion beam, wherein the ions are selected from among He, N, Ar, Kr, Xe; c) depositing a porous layer of gold (10) by electrolytic means onto the thus-treated surface of the substrate (20); d) treating the porosity of the porous layer of gold (10) by ion bombardment using an ion beam, wherein the ions are selected from among He, N, Ne, Ar, Kr, Xe. The method provides connector elements with enhanced properties.

Description

Method of manufacturing a connector element comprising a substrate on which is deposited a layer of gold

The invention relates to a method of manufacturing a connector element comprising a substrate on which a layer of gold is deposited.

"Connector element" means a part of a connector intended to make electrical contact with another part; the connectors generally comprise male or female parts intended to be placed in contact with other parts, respectively female or male, of another part. In general, a connector member is made from a metal strip or bar on which metal deposits are made. They can be shaped, in particular by machining, cutting, folding, or any other suitable technique, in order to obtain a desired form of connector element. Connector elements have many applications in electrical devices, as well as in electronic circuits.

For example, a standard connector element comprises three superimposed main parts:

a substrate, especially of copper. It is noted that copper naturally develops a layer of insulating oxide in prolonged contact with the air. It is advisable to cover the copper to avoid this inconvenience. It is also possible to use brass as a substrate and to obtain a softer substrate than a pure copper substrate;

a nickel deposit generally of thickness of at least 1.2 to about 4 microns. It serves as a diffusion barrier and can compensate for the low hardness of the gold deposit which is by nature relatively soft. This electrolytic deposit of nickel has an adverse environmental impact that often makes the use of water reprocessing stations necessary. In addition, the electrolytic nickel deposition process slows down the production speed of the connector elements. Finally, the porosity of the nickel electrolytic deposition may have an initiating effect on the porosity of the electrolytic deposition of gold. an electrolytic deposit of gold in general of 0.1 to 0.8 μm in thickness, or even up to 1.2 μm in thickness in the case of automotive connections where it is sought to reduce the thickness without degrading its porosity, in other words without reducing its anti-corrosion character. These connector elements although widely used in many industries have drawbacks. They are sensitive to degradation mechanisms that can lead to their decommissioning. The steps in this process are likely to be as follows: Aggressive chemical compounds in the air (such as sulphides or chlorides) infiltrate the porosities of the gold and nickel layer. They can produce on the contact surface the appearance of extremely hard corrosion residues. These same residues can cause under the effect of mechanical vibrations an abrasion of the contact surfaces. This can result in an increase in the roughness of the contact surfaces which can in turn induce an increase in the contact resistance. Local heating may take place and cause interatomic diffusion of the layers. Intermetallic growths are likely to occur in each layer and can give rise to internal shear forces that may create gaps in the layers that are likely to amplify the heating phenomenon. Lateral displacements of the contact surfaces can occur and enhance the wear phenomena produced by the mechanical vibrations. Eventually, the connector element is degraded and no longer performs its function.

Gold is a metal known for its qualities of stainless, its insensitivity to corrosive agents such as sulfuric acid. The regal water is one of the rare mixtures allowing the attack of gold. Gold is a good electrical conductor. Its conductivity is only slightly worse than that of copper.

Because of its qualities, the connector industry uses gold extensively as an anti-corrosion coating to protect the connector elements while maintaining their ability to pass current. In the field of connectivity, the deposit of gold is usually done electrolytically.

The gold deposit is then in the form of a lamellar structure traversed in places by opening pores which have the effect of limiting or even destroying its anticorrosion power. The formation of these pores is inherent to the gold deposition process by the electrolytic route. These pores tend to form all the more easily as the thickness of gold is low.

Currently, the gold deposits are about 0.8 microns and have a porosity resulting in pores whose diameters can reach 1 micron. As seen previously, the connector elements operate in air which generally contains a small amount of SO ₂ , NO ₂ and Cl ₂ . The porosity of the gold deposits is likely to pass these corrosive agents which eventually form on the surface of the connector elements corrosion products consisting of nitride, sulfate and chloride copper, nickel or zinc. The appearance of these corrosion products can cause a malfunction of the connector element.

For an economic question the connector industry is trying to reduce the thickness of deposits, including the gold layer. Passing the gold thickness from 0.8 μm to 0.2 μm is equivalent to dividing the cost of the deposit by a factor of 4. This objective is hampered by technical constraints: it has been generally noted that a decrease in the thickness of the deposit leads to greater porosity, which has the effect of reducing the service life of the connector element.

In addition, the presence of a nickel deposit on copper leads to constraints in terms of material cost, environmental cost and slowing down the manufacturing process of the connector elements.

The invention aims to overcome the limitations, disadvantages and technical problems described above.

The invention thus proposes a method of manufacturing a connector element comprising a substrate on which is deposited a gold layer comprising the following successive steps: a) supplying a substrate; b) ion beam bombardment treatment with a surface of the substrate where the ions are selected from the ions of the atoms of the list consisting of helium (He), nitrogen (N), argon (Ar), krypton (Kr), xenon (Xe); c) depositing a porous gold layer electrolytically on the thus treated surface of the substrate; d) ion bombardment treatment with an ion beam of the porosity of the porous gold layer where the ions are selected from the ions of the atoms of the list consisting of helium (He), nitrogen (N) ), neon (Ne), argon (Ar), Krypton (Kr), xenon (Xe).

The term "gold layer" means a layer composed essentially of gold or gold alloy.

It is thus possible thanks to step d) of the present process to reduce or eliminate the porosity of the gold deposit which are coated substrates used in the connection.

In the context of the present invention, the term "ion beam" means ions originating from one or a plurality of ion sources and directed towards the same target. An ion beam from a plurality of sources thus consists of a plurality of elementary beams. Thanks to the process of the present invention, the treatment of the porosity of the gold deposit makes it possible to retain the initial electrical, thermal and mechanical properties.

Thanks to the process of the present invention, the treatment of the gold deposit, preserves the initial color. Thanks to the method of the present invention, the treatment of the substrate and the gold deposit does not require long processing times.

With the method of the present invention, the treatment of the substrate and the gold deposit is inexpensive and allows its use in an industrial setting, its cost should not be prohibitive compared to the costs of other processes. In addition, the present method preserves the geometry of the connector elements and avoids the risk of unwanted deformations. Moreover, the treatment of a surface of the substrate in step b) makes it possible to limit the risks of corrosion of this substrate and / or to increase the hardness thereof. Ion bombardment treatment with an ion beam of a surface of the substrate and the porous gold layer provides the designer of a connector element with multiple new possibilities and allows it to overcome the usual constraints of design that usually limited the proposed configurations. It is thus possible in particular to reduce the thicknesses of the nickel and / or gold layers. It is even possible to completely get rid of the nickel layer.

According to one embodiment of the present invention, a surface of the ionically bombarded substrate in step b) is copper or copper alloy. This surface of copper or alloy is generally that on which the gold will be deposited. It is also possible to treat a copper or copper alloy surface on which a layer of nickel will be deposited before the deposit of the gold.

The ionic bombardment treatment of the copper surface can be carried out under the following conditions:

the ions of the beam of step b) are chosen from the ions of the atoms Ar, Kr, Xe and their energy is between 10 keV and 400 keV; according to one embodiment, the dose of ions thus implanted is between 10 ¹⁵ ions / cm ² and 10 ¹⁸ ions / cm ² ; the ions of the beam of step b) are ions of nitrogen atoms, N, and their energy is between 10 keV and 400 keV; according to one embodiment, the dose of ions thus implanted is between 10 ¹⁶ ions / cm ² and 10 ¹⁸ ions / cm ² ;

the ions of the beam of step b) are ions of helium atoms, He, and their energy is between 10 keV and 400 keV; according to a mode of realization, the dose of ions thus implanted is between 10 ¹⁵ ions / cm ² and 10 ¹⁸ ions / cm ² .

According to one embodiment of the present invention, a surface of the substrate treated by ion bombardment in step b) is made of nickel or nickel alloy, for example deposited electrolytically on a surface of copper or copper alloy .

The surface treatment of nickel or nickel alloy can be carried out under the following conditions considered one by one or in combination: the ions of the beam of step b) are chosen from the ions of the atoms of

He, N, Ne, Ar, Kr, Xe and their energy is between 10 keV and 400 keV;

the dose of ions implanted in the nickel or the nickel alloy is between 10 ¹⁵ ions / cm ² and 10 ¹⁸ ions / cm ² . According to one embodiment of the present invention, the porous gold layer is treated in step d) with an ion beam whose incidence angle (α) is between a minimum angle of incidence ( α _m ) and substantially 80 °, where the angle of incidence (α) of the beam is measured relative to the normal to the surface of the porous gold layer to be treated and where the minimum angle of incidence (α _m ) is determined as a function of the radius (R) of the pores and the thickness (e) of the gold layer to be treated according to the formula: α _m = arc tg (R / e)

The choice of the angle of incidence in the mentioned range makes it possible to optimize the rearrangement conditions of the material of the porous metal deposit, and the experiments carried out by the inventors have shown that, thanks to this choice, it is possible to fill the gap. porosity of metal deposition, in particular gold deposits obtained by the electrolytic route.

According to another embodiment, the angle of incidence (α) of the ion beam is substantially coincident with the normal to the surface of the metal deposit to be treated. Under these conditions, it is found that the rearrangement of the material of the porous metal deposit is less effective than under the above conditions. This lower efficiency can be compensated by a rearrangement of the surface of the substrate. Indeed, when the angle of incidence of the beam is substantially coincident with the normal to the surface of the metal deposit, the inventors were able to see that the beam ions could propagate through the pores of the deposit and reach the substrate. This effect is very significant when the pores are substantially cylindrical in shape and open on the surface of the metal deposit and on the surface of the substrate. The ions interacting with the substrate are then likely to allow ion implantation in the substrate to improve its properties of hardness and / or corrosion resistance.

According to one embodiment, the ion beam of step d) is oriented in two opposite directions with respect to the normal to the surface of the porous gold layer to be treated, in the same plane substantially perpendicular to said surface . According to this embodiment, a beam can be oriented successively in two opposite directions with respect to the normal or several elementary beams of the same ion beam can be simultaneously oriented in two opposite directions with respect to the normal to the surface of the beam. the gold layer to be treated. The inventors have found that under these conditions, the efficiency of the porosity treatment is greatly improved compared to the use of a beam oriented in a single direction.

According to another embodiment, the ion beam of step d) is oriented relative to the surface of the porous metal deposit at a plurality of angles of incidence and / or a plurality of planes substantially perpendicular to the surface. of the metal deposit to be treated. According to this embodiment, a beam can be oriented successively at a plurality of angles of incidence and / or a plurality of planes substantially perpendicular to the surface of the metal deposit or several elementary beams of the same ion beam can be simultaneously oriented at a plurality of angles of incidence and / or a plurality of planes substantially perpendicular to the surface of the metal deposit.

The inventors have also found that this embodiment makes it possible to very significantly improve the efficiency of the treatment. According to one embodiment, combining the two embodiments mentioned above, the ion beam of step d) is oriented successively at the same angle of incidence α, and in four directions which are deduced by a rotation of 90 ° with respect to the axis perpendicular to the surface, namely with respect to the normal to the surface of the metal deposit to be treated. According to different embodiments relating to step d), which can be combined:

the total dose of implanted ions is calculated so as to allow at least once the displacement of each metal atom in the implantation depth; the dose of ions implanted in the gold layer is between

10 ¹⁵ ions / cm ² and 10 ¹⁸ ions / cm ² ;

the extraction voltage of the ion beam is greater than or equal to 10 kV.

The calculation of a dose of ions as a function of a displacement chosen for a given metal is based on the principles of physics of the interactions of particles with matter. Methods and data for making such calculations are disclosed in the publications "The Stopping and Range of Ions in Matter" by JF Ziegler, Volumes 2-6, Pergamon Press, 1977-1985, "The Stopping and Range of Ions in Solids". By JF Ziegler, JP Biersack and U. Littmark, Pergamon Press, New York, 1985 (new edition in 2009) and JP Biersack and L. Haggmark, Nucl. Instr. and Meth., vol. 174, 257, 1980.

In addition, software has been developed and marketed in order to facilitate or perform such calculations, such as the software marketed under the names "SRIM" ("The Stopping and Range of Ions").

Matter ") and" TRIM "(" Transport of Ions in Matter "), developed in particular by James F. Ziegler. Note that in order to limit the volume and complexity of the equipment used, it may be desirable to limit the extraction voltage of the ion beam of step d) to at most 400 kV.

According to one embodiment, the ion beam of step b) and / or step d) is emitted by a cyclotron resonance source (ECR).

Without wishing to be bound by any scientific theory, one can propose the following mechanism to account for the advantageous effects of the treatment of the gold layer in step d), according to the invention: when an accelerated ion enters a material, it gives up by atomic collision a part of its energy to the atoms situated in its path. These atoms in turn cause collisions that provide a cascading ballistic mixing of the material.

This ballistic mixing is all the more effective as the incident ion is heavy. This ballistic mixing is evaluated by the number of collisions per unit of travel that an incident ion can cause in a given material.

For example, for a helium ion implanted with an energy of 70 keV in gold, this number is estimated at 0.015 atoms / Angstrom. As its course is 4000 Angstrom in gold, the helium ion jostles 60 atoms in its path. A nitrogen ion implanted with an energy of 70 keV in gold jostles 0.35 atom / Angstrom on a course of 1800 Angstrom, or 630 atoms. It is found that for the same energy, the efficiency of the nitrogen ion is 10 times higher than that of helium but nevertheless on a path twice as important.

According to this example, and based on these figures, it is estimated that a dose of 10 ¹⁶ helium ions / cm ² suffices to jostle 4 times each gold atom located in a 4000 Angstrom implantation thickness. For the same dose of nitrogen ions, forty times each atom in a thickness of

2000 Angstrom. In both cases, these doses are sufficient to allow the implantation layer to be totally stirred up and partially or completely fill the pores present in the gold deposit. These doses do not change the composition of the gold deposit to the extent that they represent only about 1 percent of the gold atoms.

By way of example, it can be seen that the porosity of electrolytically deposited gold deposits is a pore distribution whose diameter can vary from 0.01 μm to 1 μm through a thickness of approximately 0.8 μm. We seek to reduce these thicknesses to 0.2 microns.

Pore sizes smaller than 0.01 μm are not considered to be sites that may lead to corrosion or pitting, which could significantly damage gold deposits. According to one embodiment, the method of the invention proposes to treat the gold deposit with a dose of ions that makes it possible to stir at least once the implantation thickness. The ions have an energy which must allow them to cross partially or totally the deposit. The treatment is more effective than the implantation depth, so the energy of the ions is high. The inventors have furthermore found that it may be advantageous to reduce the thickness of gold to allow nitrogen ions to treat not only the ballistic mixing deposit but also the substrate. This treatment may be a complementary treatment to that of step d). In fact, the nitrogen ions implanted in the substrate can, by their action, retard corrosion. For example, it could be treated with nitrogen ions of 70 keV. It would then have a ballistic mixing to waterproof the 0.1 micron gold deposit and a 0.1 micron corrosion barrier in the substrate.

According to one embodiment, the method of the invention proposes to treat the metallic deposit, in particular of gold, with four doses, under the same angle of incidence and successively in four directions which are deduced by a rotation of 90 ° by relative to the axis perpendicular to the surface. Each dose preferably makes it possible to jost at least once the atoms contained in the thickness of the deposit. The minimum angle of incidence of the beam can be determined so that its tangent is equal to the ratio of the pore radius by the thickness of the gold deposit. For example, if the radius is 0.5 μm and the thickness of the deposit is 0.5 μm, the beam has an angle of incidence of minus 45 °. There is then an increase in the efficiency of ballistic mixing.

According to various embodiments relating to step d) of the method of the invention, the implantation strategy may be the following: - For the high angles of incidence, that is to say substantially grazing relative to the surface, there is it is preferable to use light ions such as helium which has the advantage of penetrating deeper into the apparent thickness of the gold deposit and to limit the risks of spraying. It is advantageous to ensure that the dose of helium ions does not exceed a few percent to limit the modification of the composition of the gold deposit from an electrical, mechanical or aesthetic point of view.

- For lower angles of incidence it may be better to choose heavier ions such as nitrogen given the efficiency they have in brewing the gold deposit. This reduces the processing times. In this case, the necessary doses are low and there is little risk of modifying the electrical, mechanical or aesthetic characteristics of the deposits.

In addition, it is found that by decreasing the thickness of the gold deposits, the average radius of the pores is increased. For the treatment, it is possible to progressively evolve from the use of nitrogen ions to helium ions, to the extent that the angles of incidence are increased.

To increase the efficiency of gold deposition treatment while reducing its cost, the method of the invention recommends according to one embodiment, the use of cyclotron resonance sources known as RCE. These sources have the particularity to be compact and produce multicharged ions, so more energy for the same extraction voltage. In addition, these sources are robust and consume little electricity. Given their size, these sources can be arranged in series or in parallel to increase the processing capacity of the machines. Their intensities, of the order of 10 mA, allow bands a few mm wide at speeds of the order of a few meters per minute. These processing speeds are acceptable for the industry. The process of the invention proposes, by way of examples, to treat the porosities of gold deposits. It can be used with other metals that have similar porosity problems.

The energy of the ion beam is preferably greater than or equal to 10 keV. Such energy is selected because it allows to create cascades of atoms following the impact of the ions.

By way of example, the following treatment conditions for step b) are proposed:

in particular with a view to improving the surface condition of the copper: Ar ions can be implanted at an incidence of 45 to 80 °, with an energy of

10 keV to 20 keV, and with a dose of 10 ¹⁶ to 10 ¹⁸ ion / cm ² ;

- in particular to improve the resistance to oxidation and corrosion of copper: we can implant N ions at an incidence of 0 °, with an energy of 50 keV to 300 keV, and with a dose of 10 ¹⁷ to 4.10 ¹⁷ ion / cm ² ; in particular with a view to hardening a copper surface: He ions can be implanted at an incidence of 0 °, with an energy of 50 keV to 100 keV, and with a dose of ¹⁶ to 10 ¹⁷ ion / cm ² ;

in particular with a view to reducing the porosity of a nickel deposit and improving the interfacial adhesion: for a nickel deposit with a thickness greater than or equal to 0.2 μm, it is possible to implant he ions, with 4 incidences at 45 °, with an energy of 50 keV to 100 keV and with a dose of 10 ¹⁶ to 10 ¹⁷ ion / cm ² ;

• for a thickness of nickel deposit between 0.1 .mu.m and 0.2 .mu.m: can be implanted N ions, with 4 impacts at 45 °, with an energy of 50 keV to 250 keV and with a dose 5.10 ¹⁵ at 5.10 ¹⁶ ion / cm ² ;

• for a nickel deposit less than or equal to 1 μm in thickness: Ar ions can be implanted with 4 incidences at 45 °, with an energy of 50 keV at 400 keV and with a dose of ¹⁵ to 10 ¹⁶ ions / cm ² . By way of example, the following processing conditions are proposed for step d):

for a gold deposit of 0.1 .mu.m thick, a nitrogen beam perpendicular to the deposit and energy of the order of 60 keV, or of higher energy, allows both efficient mixing and the crossing of the depot;

for a gold deposit 0.4 μm thick, a helium beam perpendicular to the deposit and energy of the order of 100 keV, or of higher energy, allows both efficient mixing and crossing the depot.

By way of example, Table 1 gives examples of choice of parameters for the treatment of porosity in a gold layer, as a function of the ion used (helium or nitrogen), the thickness, e, the deposit gold, radius, R, pores to be treated. We report "α _m " corresponding to the minimum angle of incidence,

"L" corresponding to the path of the ion to cross the deposit, "E _mn " corresponding to the minimum energy required to cross the deposit, the ratio "A" corresponding to the displacement of atoms by Angstrom and by incident ion, the value "D" corresponding to the dose required to move once each atom of the thickness of the deposit (expressed in 10 ¹⁶ ions per cm ² ) and the value "ep" of the thickness sprayed (in Angstrom). The data mentioned correspond to treatments with an ECR source where the extraction voltage is 45 kV. Thus, Keke and He2 + helium He + ions of 90 keV or nitrogen ions mainly in the form of N + of 45 keV, N2 + of 90 keV, N3 + of 135 keV are obtained.

In addition, the inventors have found that it may be advantageous to limit to about 5% atomic concentration, the amount of implanted ions in step d) in particular in the case of helium.

In addition, the inventors have found that the treatment by ion bombardment of the substrate and the gold layer was advantageous in terms of hardness. By way of example, the hardness of the gold layer (from 2 GPa to 4 GPa) or a nickel deposit (from 3 GPa to 6 GPa) or a copper surface (from 1 2 GPa at 2.5 GPa) by implantation of helium ions.

This advantageously results in an increase in the corrosion resistance of each of the layers thus treated.

There is also enhanced interfacial adhesion when the ion has sufficient energy to pass through a first layer and create an ionic mixture in a wafer at the interface of the first layer and the second layer. This slice measures about 10 nm and corresponds to the size of the atomic cascades generated by the atomic collisions of the incident ions.

Advantageously, it is possible to combine the effects mentioned above. By way of example, and without wishing to be bound by any scientific theory, one can think that the effects accumulate layer by layer for the hardnesses while the effects multiply layer by layer for the resistance to corrosion. It can be estimated that the overall hardness of a connector element is the sum of the hardnesses of the different layers weighted by their respective thicknesses. If the hardness of a layer of nickel is multiplied by two, it is possible to reduce by 2 the value of its thickness without altering its mechanical behavior under the effect of the same load. If the hardness of the nickel-gold layer is multiplied by 2 and separately, the nickel-gold complex is multiplied by 2. For corrosion resistance, it can be considered that the corrosion resistance of a layer is inversely proportional to the probability that a chemical agent will pass through that layer in a given time. In fact, the corrosion resistance of two superimposed layers numbered 1 and 2 is inversely proportional to the probability that a chemical agent will pass through layer 1 and layer 2, the product of layer 1 and layer resistances. 2. If layer 1 and layer 2 have a corrosion resistance multiplied by 4 after treatment, then the corrosion resistance of these two layers is then multiplied by 16. On the other hand it is expected that the probability that a chemical agent will cross a layer in a given time inversely proportional to the thickness of this layer. By way of example, reducing the thickness of a layer by a factor of 2 reduces the corrosion resistance by a factor of two since the flux of chemical agent released through the layer is twice as great. . By way of example, it is proposed to use low-dose bombardment with He, N, Ar ions in order to obtain amorphization curing. This type of treatment can be extended to Ne, Kr, Xe ions. When the thickness of the deposit decreases, heavier ions such as Ar, Kr or Xe are preferably chosen, which have a higher amorphization power at the same dose but in a lesser thickness, which reduces the processing time. High-dose N-bombardment is aimed at creating a corrosion-resistant diffusion barrier.

The invention also relates to a connector element comprising a substrate and an electrolytically-obtained porous gold layer in which the substrate comprises a copper strip on which a layer of nickel has been deposited and where the porous gold layer has been deposited. deposited on said nickel layer, and wherein the nickel layer comprises implanted atoms selected from the list consisting of helium (He), nitrogen (N), argon (Ar), krypton (Kr), xenon (Xe), the porous gold layer comprises implanted atoms selected from the list consisting of helium (He), nitrogen (N), Neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and in that the thickness of the nickel layer is less than or equal to 1 μm, for example less than or equal to 0.5 μm, or even less than or equal to 0.2 μm.

According to another embodiment, the invention also relates to a connector element comprising a substrate and an electrolytically-obtained porous gold layer in which the substrate comprises a copper strip on which the porous gold layer has been deposited, wherein the surface of the copper strip comprises implanted atoms selected from the list consisting of helium (He), nitrogen

(N), argon (Ar), krypton (Kr), xenon (Xe), the porous gold layer comprises implanted atoms, selected from the list consisting of helium (He), nitrogen

(N), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe). A standard connector element, later named CS, in the automotive industry includes a brass substrate that is less conductive than copper and less prone to corrosion, a 1.2 micron nickel electrolytic deposit, a gold deposit of 1, 2 micron. By way of example, the method of the invention proposes to replace this standard connector element CS by a connector element according to the invention, hereinafter called Cl, consisting of a preferably pure copper substrate. 0.4 micron electrolytic nickel plating and 0.4 micron gold electroplating. By applying the previously explained treatment procedure, in addition to the material cost reduction, the following characteristics are obtained.

- At the level of the overall hardness (sum of the hardnesses of each layer weighted by their thickness expressed in unit without dimension):

• we can estimate the overall hardness for the connector element Cl: hardness Cl = 0.4 x 4 GPa + 0.4 x6 GPa + 0.4 x 2.5 GPa = 5 GPa

• we can estimate the overall hardness for the CS connector element: hardness CS = 1, 2 x 2 GPa + 1, 2 x 2 GPa + 0.4 x 1, 2 GPa = 5.3 GPa

It is noted that the overall hardnesses of the connector element C1 and the standard connector element CS are substantially comparable. However, in the case of the connector element C1, there is an improvement in the modulus of elasticity and the interfacial adhesion of the layers.

- At the level of corrosion resistance:

• for the Cl connector element, the corrosion resistance of two 0.4-micron gold-nickel layers treated separately is estimated to be

• corrosion resistance Cl = 2,8 x 2,8 = 7,84 • for the standard connector element, CS, the corrosion resistance of two gold-nickel layers of approximately 1, 2 micron each is estimated at :

• corrosion resistance CS = 1, 44 x 1, 44 = 2.07 It is therefore noted that the corrosion resistance is 4 times greater for the connector element C1 than for the standard connector element CS. It is even possible to further increase this gap if we add the treatment of the copper substrate by implantation of nitrogen. Among the advantages offered by the present invention, and without wishing to be bound by any scientific theory, we can note the following points that are likely to improve a driver of the state of the art, or even able to stop its degradation:

• the path of the chemical compounds through the treated gold layer, and possibly nickel if it is treated, is made very difficult since the one (s) is (are) less porous (s);

• the formation of surface corrosion residues is greatly reduced since the copper and the other atoms of the substrate, including possibly nickel, have difficulty going up through the gold layer thus treated;

The contact surface becomes more resistant to abrasive wear since the production of corrosion residues is reduced and furthermore the contact surface is likely to have a mechanically reinforced hardness; • the contact resistance changes little over time, since the risks of degradation of the contact surface decrease;

• the risk of overheating is reduced since the risks of increasing the contact resistance decrease;

• thanks to the treatment of the substrate, the mobility of the ions of the substrate, in particular of copper and / or of nickel, is strongly diminished, even stopped on the surface of the substrate since a diffusion barrier is interposed with the passage of the ions;

• it can be furthermore thought that the risk of delamination of the layers is likely to be reduced since the treated layers are more homogeneous, their modulus of elasticity is, in general, improved and that they should adhere better to each other because of the process of ionic mixing at the interfaces under the effect of ion bombardment.

The following example describes a connector element proposed by the method according to the invention to replace a standard connector element. A copper or brass strip is bombarded with argon to improve the surface state, nitrogen to a thickness of 0.2 micron to create a corrosion barrier, then with helium to a thickness of 0 , 4 micron to produce hardening. A layer of nickel is deposited on copper or brass with a thickness of 0.4 micron and is bombarded with helium to a thickness of 0.4 micron, to increase its hardness and reduce its porosity. For example, ions such as argon will be chosen to very quickly treat 0.1 micron thicknesses and nitrogen ions to treat thicknesses of 0.2 microns. A layer of gold is deposited on the nickel layer and has a thickness of 0.4 microns. It is bombarded with helium to a thickness of 0.4 micron to increase its hardness and reduce its porosity. As before, for example, ions such as argon will be chosen to very quickly treat thicknesses of 0.1 micron and nitrogen ions to treat thicknesses of 0.2 microns. The ion bombardment mixture provides good cohesion at the interface between the gold layer and the nickel layer and at the interface between the nickel and the substrate.

According to another example, the connector element according to the invention is devoid of a nickel layer and the treatments of copper or brass, and gold are identical to those indicated above. Other features and advantages of the present invention will appear in the following description of nonlimiting exemplary embodiments with reference to the accompanying drawings in which:

FIG. 1 is a schematic sectional view of a gold deposit on a substrate; FIG. 2 is a diagrammatic sectional view of the implementation of the method according to the invention; FIG. 3 is a view of potentiometric curves of samples treated according to the invention and of a comparative sample,

- Figure 4 is a view of a device for implementing the present invention. For the sake of clarity, the dimensions of the various elements shown in these figures are not necessarily in proportion to their actual dimensions.

FIG. 1 represents a porous gold deposit 10, of thickness e, deposited on a substrate 20. Several types of porosity can exist in the porous gold deposit 10.

In the case of electrolytic deposits, it is found that the porosities develop essentially in a direction perpendicular to the surface of the substrate on which the deposit is made. For example, the porosities 30 are substantially cylindrical and open on both the substrate and the outer surface of the gold deposit. Porosities 32, 36 are closed porosities formed respectively within the gold deposit or at the interface with the substrate.

Porosities 34 are pores that open onto the outer surface of the metal deposit but do not open onto the substrate.

The porosities are able to pass corrosive agents and cause corrosion of the substrate.

The substrate 20 is for example a copper strip or according to another embodiment, a copper strip coated with an electrolytically deposited nickel layer.

The method according to the invention aims to fill these porosities 30, but is also likely to allow rearrangements of material capable of filling the porosities 32, 34, 36.

It also aims to improve the surface of the substrate on which the gold deposit is made.

Figure 2 shows the treatment of a pore with an ion beam F. The metal deposit 10 is formed on a substrate 20 and its thickness e is determined between the lower face 12 of said deposit in contact with the substrate and the outer opposite face 14. A pore 30 is shown, of cylindrical shape and limited by its wall 35 and its bottom 37 corresponding to an area of the substrate 20 on which the gold deposit 10 is deposited.

In order to fill, at least partially, this pore 30, an ion beam F is directed on the surface 14 of the deposit. The beam is oriented at an angle α, determined with respect to the normal to the surface 14, where α is greater than an angle α _m of minimum incidence which has the tangent ratio of the radius R of the pore by the thickness e of the deposit of gold.

When the ions of the beam F bombard the surface 14, in particular according to the selected incidence, the atoms located at the edge of the pore are stirred and may fill the pore. The dotted form is the profile of the pore filled by the atoms which have been stirred on the edges of the pore during implantation. The atoms initially present in the zone 16, located between the profile 15 and the wall 35 are moved and fill the area 17 between the profile 15 and the initial bottom 37 of the pore. In the example shown, the gold deposit is subjected to two beams oriented at an angle α, in the same plane perpendicular to the surface 14. It can be seen that this configuration advantageously makes it possible to fill the pore 30.

Note that when the angle of incidence is greater than the minimum angle of incidence, the bottom of the pore is filled more effectively than when the angle of incidence equals the minimum angle of incidence, but it is necessary in return that the energy of the ions is sufficient to cross the apparent thickness which at the same time increases.

FIG. 3 represents the potentiometric curves obtained for:

a virgin gold deposit constituting a comparative sample, curve 41;

a deposit of gold treated according to the invention by a perpendicular nitrogen beam, curve 42; a deposit of gold treated according to the invention by a helium beam, curve 43, at an angle of 45 ° and in four perpendicular directions.

Gold deposits were electrolytically deposited on a nickel substrate. The deposited gold has a thickness of 0.8 μm and corresponds to pure gold. The solution used is 0.5 M H ₂ SO _4. The corrosion current is reduced by a factor of 2 for nitrogen, by a factor of 3 to 4 for helium. In both cases, this decrease in the corrosion current reflects the decrease in the porosity due to the treatment. The implanted nitrogen dose is four times that of helium. However, a higher efficiency of the treatment with helium is observed. This is explained by the optimization of the ballistic mixing obtained in four perpendicular directions, and under the same angle of incidence of 45 °.

Fig. 4 shows a tape-running processing machine. The band 60 consists of a substrate and a porous gold deposit to be treated. For a tape-running processing machine, a differential vacuum column 56 should be placed between the ECR source 55. Indeed, a vacuum of 10 ^-6 mbar is required for the production of the plasma in the source and a vacuum of 10 ^"4 mbar is sufficient to treat the strip in the chamber 57. The function of the differential vacuum column 56 is to let the beam F pass while preventing the rise of gases in the plasma chamber. The differential vacuum column 56 is equipped with a turbomolecular pumping system for trapping these gas lifts. Two locks, one input, the other output, are equipped with a primary pump system 51 and 54 and turbomolecular 52 and 53 to allow the band 60 to pass and create a vacuum in the treatment chamber 57 .

During a first pass, it is possible to treat a surface of the substrate, for example copper or nickel, then electrolytically deposit the gold on the substrate thus treated, and proceed to a second pass of the substrate coated by the gold to treat this layer of gold. The unwinding speed of the web on the unwinder / rewinder 58, 59 is calculated so as to obtain the dose required to treat the substrate and / or the gold deposit. To avoid a risk of overheating which could create a rupture of the band, it is possible to increase the running speed and proportionally increase the number of passes in forward and reverse.

The invention is not limited to the exemplified embodiments and should be interpreted in a nonlimiting manner and encompassing any equivalent embodiment. It should be noted that if examples of gold deposits have been presented, the method according to the invention is also likely to reduce, or even fill, the porosity of deposits of other metals, for example silver, nickel , platinum, zinc, tin or alloys deposited on a substrate to form a connector member.

Claims

1. A method of manufacturing a connector element comprising a substrate on which is deposited a gold layer characterized in that it comprises the following successive steps: a) supplying a substrate (20); b) an ion beam ion beam treatment of a surface of the substrate (20) wherein the ions are selected from the ions of the atoms of the list consisting of helium (He), nitrogen (N); ), argon (Ar), krypton (Kr), xenon (Xe); c) depositing a porous gold layer (10) electrolytically on the thus treated surface of the substrate (20); d) ion bombardment treatment with an ion beam of the porosity of the porous gold layer (10) wherein the ions are selected from the ions of the atoms of the list consisting of helium (He), the nitrogen (N), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe).

2. A method of manufacturing a connector element according to the preceding claim characterized in that a surface of the substrate treated by ion bombardment in step b) is copper or copper alloy.

3. A method of manufacturing a connector element according to the preceding claim characterized in that the dose of implanted ions is between 10 ¹⁵ ions / cm ² and 10 ¹⁸ ions / cm ² .

4. A method of manufacturing a connector element according to any preceding claim characterized in that a surface of the ionically bombarded substrate in step b) is made of nickel or nickel alloy, for example deposited electrolytically on a surface of copper or copper alloy.

5. A method of manufacturing a connector element according to the preceding claim characterized in that the dose of implanted ions is between 10 ¹⁵ ions / cm ² and 10 ¹⁸ ions / cm ² .

6. A method of manufacturing a connector element according to any one of the preceding claims characterized in that the porous gold layer is treated in step d) with an ion beam whose incidence angle (α) is between a minimum angle of incidence (α _m ) and substantially 80 °, wherein the angle of incidence (α) of the beam is measured relative to the normal to the surface (14) of the porous gold to be treated and where the minimum angle of incidence (α _m ) is determined according to the radius (R) of the pores and the thickness (e) of the gold layer to be treated according to the formula:

7. A method of manufacturing a connector element according to any one of claims 1 to 5 characterized in that the gold layer is treated in step d) with an ion beam whose angle d incidence (α) is substantially coincident with the normal to the surface (14) of the gold layer to be treated.

8. A method of manufacturing a connector element according to any preceding claim characterized in that the ion beam of step d) is oriented in two opposite directions relative to the normal to the surface (14) of the porous gold layer to be treated, in the same plane substantially perpendicular to said surface (14).

9. A method of manufacturing a connector element according to any preceding claim characterized in that the ion beam of step d) is oriented relative to the surface (14) of the gold layer porous at a plurality of angles of incidence and / or a plurality of planes substantially perpendicular to the surface (14) of the gold layer to be treated.

10. A method of manufacturing a connector element according to claims 8 and 9 characterized in that the ion beam of step d) is oriented successively at the same angle of incidence α, and in four directions which deduce by a rotation of 90 ° with respect to the axis perpendicular to the surface, namely with respect to the normal to the surface (14) of the gold layer to be treated.

A method of manufacturing a connector element according to any one of the preceding claims, characterized in that the total dose of ions implanted in step d) is calculated so as to allow at least once the displacement of each metal atom in the implantation depth.

12. A method of manufacturing a connector element according to any one of the preceding claims characterized in that the extraction voltage of the ion beam is greater than or equal to 10 kV, for example less than or equal to 400 kV.

13. A method of manufacturing a connector element according to any preceding claim characterized in that the ion beam of step b) and / or step d) is emitted by a resonance source cyclotronic (RCE) (55).

A connector element comprising a substrate and an electrolytically-obtained porous gold layer where the substrate comprises a copper strip on which a layer of nickel has been deposited and where the porous gold layer has been deposited on said layer nickel, characterized in that the nickel layer comprises implanted atoms selected from the list consisting of helium (He), nitrogen (N), argon (Ar), krypton (Kr), xenon (Xe), the porous gold layer comprises implanted atoms selected from the list consisting of helium (He), nitrogen (N), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and in that the thickness of the nickel layer is less than or equal to 1 μm, for example less than or equal to 0.5 μm, or even less than or equal to 0, 2 μm.

A connector element comprising a substrate and an electrolytically-obtained porous gold layer where the substrate comprises a copper strip on which the porous gold layer has been deposited, characterized in that the surface of the copper strip comprises implanted atoms selected from the list consisting of helium (He), nitrogen (N), argon (Ar), krypton (Kr), xenon (Xe), and porous gold layer comprises implanted atoms selected from the list consisting of helium (He), nitrogen (N), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe).