EP0586300A1 - Electrical nickel contact terminal for connector, connector and method of manufacturing same - Google Patents

Abstract

This terminal possesses, in its contact region, a thickness of nickel essentially devoid of metallic surface coating, this thickness of nickel being coated with a layer of a lubricating agent bonded to the nickel. The lubricating agent may be especially a fluorinated polymer, such as a poly(perfluoroalkylether) or a non-fluorinated polymer, such as a poly(phenylether). It has a contact resistance of less than 400 m OMEGA and a friction coefficient of less than 0.4, these criteria being fulfilled from the first connection operation and during at least 50 successive connection/disconnection operations, preferably at least 500 successive operations. A suitable method comprises the steps consisting in: (a) manufacturing a contact terminal having a thickness of nickel in its contact region; (b) coating this thickness of nickel with a layer of a lubricating agent; and (c) bonding the lubricating agent to the nickel, for example by polishing, beneath the lubricant, the surface of the nickel.

Description

The invention relates to connectors with contact terminals (hereinafter simply called) made of nickel, and in particular connectors for which high reliability is sought, typically of the order of several hundred connection / disconnection operations.

Such connectors are particularly advantageous, but in no way limiting, in the field of automotive equipment, where it is sought in particular to have connectors having such properties and which can be produced industrially at the lowest possible cost.

Among the low-cost connectors are those whose contact region is essentially made of a tin-lead alloy. However, this type of contact has serious deficiencies both in corrosion under vibration and in the number of operations (the reliability is limited to a few connections / disconnections), which makes it unsuitable for the desired objective (reliability guaranteed over several tens or hundreds of maneuvers).

This is why, in this context of reliability, the most commonly used contacts until now are contacts coated with gilding, which ensures both protection of the contact against oxidation and a low coefficient of friction allowing to reduce to a minimum the abrasion of surfaces during successive operations.

Contacts of this type generally consist of a brass body coated with a layer of gold of the order of one micrometer, with the interposition of a layer of nickel, generally electrodeposited, of a few micrometers. The intermediate layer of nickel prevents gold and brass from diffusing into each other, leading to oxidation of the brass going back to the free surface of the contact. Incidentally, note that nickel plays only a physicochemical role here (diffusion barrier) and does not affect the electrical and mechanical properties. proper contact (contact resistance, coefficient of friction, etc.), since it is always an underlying layer, never bare.

The contacts thus made achieve the desired reliability objectives: they easily provide several thousand operations). However, they are nevertheless expensive to produce, which reserves them for professional or high-end applications.

We tried to reduce the cost of gilding by depositing a more or less thick, more or less selective layer of gold (i.e. only part of the contact is gilded), etc., but the cost nevertheless remains high and hardly compatible with a generalization to mass production applications such as the automobile or consumer electronic devices.

Attempts have been made to produce connectors in which the contact region consists of nickel, the nickel being bare, without gilding or the deposition of another surface layer, whether these are solid nickel terminals or terminals. another metal coated with a layer of nickel electrodeposited. The contact is then a nickel-on-nickel, or nickel-on-gold contact (depending on whether the two elements of the connector are made of bare nickel, or only one).

• en premier lieu, il a tendance à se corroder par oxydation, ce qui a pour effet d'en dégrader les performances tant électriques (résistance de contact) que mécaniques (coefficient de frottement) ;
• en second lieu, il présente un très mauvais coefficient de frottement (µ de l'ordre de 1) ce qui produit une dégradation mécanique très importante de la surface : cette abrasion va créer trés rapidement - parfois même dès la première manoeuvre de déconnexion/reconnexion - une masse de débris métalliques particulaires qui vont très rapidement dégrader les performances électriques du connecteur ; de ce fait, un contact en nickel, lorsque c'est le nickel qui assure le contact électrique proprement dit (et non plus la couche d'or comme dans le cas d'un contact doré) ne permet donc en aucune façon d'atteindre le but recherché de fiabilité garantie sur un nombre de manoeuvres de, typiquement, plusieurs dizaines ou plusieurs centaines.

But nickel has two major drawbacks in this case:

• firstly, it tends to corrode by oxidation, which has the effect of degrading both electrical (contact resistance) and mechanical (coefficient of friction) performance;
• secondly, it has a very poor coefficient of friction (µ of the order of 1) which produces very significant mechanical degradation of the surface: this abrasion will create very quickly - sometimes even from the first disconnection / reconnection maneuver - a mass of particulate metal debris which will very quickly degrade the electrical performance of the connector; therefore, a nickel contact, when it is nickel which provides the actual electrical contact (and no longer the gold layer as in the case of a gold contact) therefore does not in any way achieve the desired objective of guaranteed reliability over a number of operations of, typically, several tens or several hundreds.

• l'utilisation de faibles courants, ceux-ci étant insusceptibles au moment de leur établissement, de percer la couche d'oxyde et rétablir ainsi une faible résistance de contact (c'est cette particularité qui permet notamment d'utiliser des simples contacts en laiton pour véhiculer des courants élevés, malgré leur propension à l'oxydation) et
• d'autre part et surtout, la recherche d'une faible force d'insertion pour le connecteur, cette faible force étant insusceptible de casser, par effet mécanique, la couche d'oxyde ; or, cette faible force est indispensable si l'on veut réduire au minimum la dégradation mécanique du nickel en raison de sa mauvaise tenue au frottement, comme indiqué plus haut : on aboutit donc ainsi à une contradiction technique.

In addition, two circumstances aggravate these disadvantages:

• the use of low currents, these being insusceptible at the time of their establishment, of piercing the oxide layer and thus re-establishing a low contact resistance (it is this peculiarity which allows in particular to use simple brass contacts to carry high currents, despite their propensity for oxidation) and
• secondly and above all, the search for a low insertion force for the connector, this low force being incapable of breaking, by mechanical effect, the oxide layer; However, this low force is essential if one wants to minimize the mechanical degradation of nickel due to its poor resistance to friction, as indicated above: this therefore leads to a technical contradiction.

Various workarounds have been proposed, for example the replacement of pure nickel with a nickel-palladium alloy coated with a very light gold, but this technique is ultimately still quite expensive.

The object of the invention is to overcome these various drawbacks of nickel contacts, by proposing a contact and a method of manufacturing it making it possible to achieve characteristics close to those of gold contacts - in terms of low contact resistance. , low coefficient of friction and reliability guaranteed on a very large number of operations - without being obstructed by the very high cost of gilding.

One of the aims of the invention is also to propose a connector having all these advantages and usable for low currents with low insertion forces, without these latter constraints interfering on the electrical and mechanical properties of the connector.

It will also be seen that the desired electrical and mechanical performance is obtained from the first maneuver, an important characteristic because it avoids having to carry out any preparation of the contact or of the connector before its first use.

According to a first aspect of the invention, the contact terminal of the invention, which is characterized by its structural parameters, is an electrical contact terminal comprising, in its contact region, a thickness of nickel essentially devoid of surface metal coating , this nickel thickness being coated with a layer of a lubricating agent attached to the nickel.

The lubricating agent can in particular be a fluorinated polymer such as a poly (perfluoroalkylether), or a non-fluorinated polymer such as a poly (phenylether).

The thickness of the layer of lubricating agent is advantageously between 50 and 400 nm, for a typical minimum number of successive connection / disconnection operations between 50 and 500 operations, respectively.

According to another aspect of the invention, the contact terminal, which is characterized by its intrinsic properties, is an electrical contact terminal comprising, in its contact region, a thickness of nickel essentially devoid of surface metal coating, having a resistance contact less than 400 mΩ and a coefficient of friction less than 0.4, these criteria being met from the first connection maneuver and during at least 50 successive connection / disconnection maneuvers, preferably during at least 500 successive connection maneuvers / logout.

The invention also relates to a method of manufacturing such a terminal, this method - which is in no way limiting, other implementations which can be envisaged - comprising the steps consisting in: (a) manufacturing a terminal contact having a thickness of nickel in its contact region; (b) coating this nickel thickness with a layer of a lubricating agent; and (c) attaching the lubricant to the nickel, for example by polishing the surface of the nickel under lubricant.

We will now describe examples of embodiment and implementation of the invention, with reference to the accompanying drawings.

FIG. 1 shows, for a contact made according to the teachings of the invention, the evolution of the contact resistance R _c as a function of the number N of operations, for different values of thickness of the layer of lubricant deposited.

FIG. 2 shows, for a contact made according to the teachings of the invention, the evolution of the coefficient of friction μ as a function of the number N of operations, for different values of thickness of the layer of lubricant deposited.

FIG. 3 is a curve giving, as a function of the thickness of the layer of lubricant deposited on the contact, the typical number of operations allowed under the required reliability conditions.

FIG. 4 illustrates the experimental device for measuring the contact resistance.

FIG. 5 shows comparative characteristics of contact resistance as a function of the pressing force, directly delivered by the assembly of FIG. 4, for a bare nickel contact, a gold nickel contact, lubricated or not, and a contact according to l 'invention.

We will now describe examples of implementation of the invention.

• (a) résistance de contact inférieure à un seuil de 400 mΩ (paramètre électrique);
• (b) coefficient de frottement inférieur à un seuil de 0,4 (paramètre tribologique), ceci pour garantir une usure minimale et, par voie de conséquence, le maintien de la propriété (a) précitée;
• (c) les deux propriétés (a) et (b) sont conservées pendant au moins 500 manoeuvres de connexion/déconnexion; et
• (d) les deux propriétés (a) et (b) ci-dessus sont obtenues dès la première manoeuvre, c'est-à-dire que le connecteur ne nécessite aucune préparation particulière avant sa mise en service.

In these examples, the aim sought, of course not limiting, is to produce a connector which, while being low cost (for example compatible with the economic constraints of automotive equipment), exhibits the following typical performances:

• (a) contact resistance below a threshold of 400 mΩ (parameter electric);
• (b) coefficient of friction below a threshold of 0.4 (tribological parameter), this to guarantee minimal wear and, consequently, the maintenance of the above-mentioned property (a);
• (c) the two properties (a) and (b) are retained for at least 500 connection / disconnection operations; and
• (d) the two properties (a) and (b) above are obtained from the first operation, that is to say that the connector does not require any particular preparation before it is put into service.

The numerical values given in the present description are however only indicative; we will see in particular below how we can, for example, modulate the minimum number of maneuvers according to the application considered by playing on certain parameters for implementing the method.

Example I

A connection assembly is made up, on the one hand, of a beryllium bronze ball coated with a layer of 5 μm of electrodeposited nickel and, on the other hand, of a plane brass blade also coated with a layer of nickel electrodeposited of 5 μm, thus constituting two contacts made according to the teachings of the invention, the electrical and mechanical properties of which will be determined.

Note that nickel is not necessarily electrodeposited; it can also be solid or made up of a layer deposited in another way, this characteristic in no way modifying the characteristics of the invention.

The contacts are then coated with a layer of lubricant consisting of a perfluorinated polymer such as a PFAE, that is to say a poly (perfluoroalkylether), also called or. The polymers of this family indeed have interesting properties such as: high molecular weight, good lubrication coefficient, low surface tension, low volatility, chemical inertness and hydrophobia.

These polymers are also known to be used as liquid lubricants applied to gold contacts in order to limit wear.

However, in the case of the present invention, the role of this fluid (which, for convenience, we will simply call) is not only to avoid metal-on-metal friction, and therefore to limit wear by abrasion, but also - and in a completely characteristic manner of the invention - also of limiting the oxidation of the active metal during the sliding of the contacts and thus maintaining at a low level the contact resistance, in particular by forming a bonding complex between the metal and the lubricant.

However, this latter property is never used in the conventional uses of these lubricants (application to gold contacts), the gold not oxidizing and forming no complex with the lubricant; the formation of such a complex would moreover in this case be considered a serious drawback, since it would destroy the advantages provided by the gold of the surface layer. In the case of nickel, this being a very reactive metal, it naturally clings to the molecules of the lubricant; but the oxide prevents it from doing so and it is therefore necessary to eliminate this oxide.

It is further noted that, in the case of ductile materials such as gold, the wear is essentially an adhesive wear, which means that the problem of wear debris causing abrasion is absent (unlike nickel); lubrication is then used to delay the transfer which has the effect of spreading the metal over the stroke of mechanical contact.

The application of the lubricant to the nickel of the contact can be done by different techniques. In this example, the operation is carried out by spraying a mixture comprising 50% by weight of 1% PFAE or 0.1% in solution in R113, and 50% of a propellant such as HFA. The spraying is carried out at a distance of 15 cm for a controlled period depending on the thickness of lubricant which it is desired to apply.

In the examples which will be given below, the properties for various thicknesses of lubricant, sprayed on 6 nm, 66 nm, 198 nm and 396 nm, will be compared.

Other techniques can also be envisaged, for example by dipping.

Each of the contacts is then subjected to an essential operation, consisting in destroying the surface oxide layer which was present on the nickel before the lubricant is sprayed, and in attaching or this lubricant to the nickel.

One of the possibilities for carrying out this operation consists in carrying out a simple polishing under contact lubricant, this polishing being continued until almost complete elimination of the oxide layer, this disappearance being able to be observed by obtaining, reproducibly, with an initial contact resistance less than a given value, for example less than 400 mΩ.

If the deposition of the perfluorinated polymer is carried out by soaking, the polishing may possibly be carried out directly in the bath, therefore at the same time as the deposition.

The contact thus obtained is then subjected to wear tests consisting of performing back-and-forth cycles and measuring after each cycle (simulating a connection / disconnection) the contact resistance Rc by the experimental device which will be described more far with reference to FIG. 5. The coefficient of friction μ is also measured.

For this purpose, the contact is subjected to a displacement of a length of 1 mm at a constant speed of 0.1 mm / s and a constant load of 1 N, applied in the normal direction. An appropriate tribometer measures the value of the tangential force F _T during displacement, which gives the instantaneous value of the coefficient of friction µ and makes it possible to calculate an average value per cycle of this parameter at the end of each displacement, the resistance is measured contact Rc with a four-point device, the tangential force being zero in order to measure the resistance in a stationary condition.

FIG. 1 illustrates the variations of the contact resistance R _c thus measured as a function of the number N of cycles, for the four values of thickness of lubricant considered above; FIG. 2 is equivalent to FIG. 1, for the mean coefficient of friction μ.

With regard to the contact resistance R _c , this, the value of which is - from the first operation - typically less than 5 mΩ, therefore very much below the threshold value imposed of 400 mΩ, decreases slightly during the first twenty cycles, then becomes unstable (for the smallest thicknesses of lubricant) or increases slightly (for the highest thicknesses of the lubricant) to a maximum of 30 mΩ for the thickest lubricant thickness.

With regard to the coefficient of friction µ, the curves have substantially the same shape in the four cases, with a first phase where µ remains weak and stable, followed by a second irregular phase characterized by fluctuations due to the presence at l 'interface of wear particles (oxidized) disturbing the lubrication action, then finally a phase where µ increases very quickly, significant wear creating many non-lubricated contact points; the contact then behaves like a dry nickel-on-nickel contact, with a coefficient of friction µ which has become excessive.

It is noted that the increase in thickness, and therefore in the quantity of lubricant, delays the appearance of these successive phases and therefore makes it possible to increase the number of possible maneuvers.

If one considers that the operation of the contact remains satisfactory as long as the coefficient of friction µ remains lower than a maximum value of 0.4, one can extrapolate the curve of figure 3, giving the average number N of operations allowed according of the thickness e of lubricant deposited.

In practice, depending on the envisaged application, the performance of the connector is determined in the maximum number of possible operations (for example a few tens, a few hundreds, etc.) and the thickness of the lubricant is deduced therefrom. to file correlatively.

It should be noted in this regard that a compromise must be found between a too thick and too thin a lubricant: if the thickness is too large, the lubricant will, of course, optimally absorb all the debris produced by the successive operations, but it will capture the ambient dust much more ; conversely, if the thickness is too small, the lubricant reserve will be insufficient and the debris will absorb the lubricant instead of being the reverse, thus very quickly degrading the performance of the connector.

In general (and not limiting), it can be considered that, for connectors having to withstand a typical number of 50 to 500 operations, the lubricant should be deposited on a typical thickness of the order of 50 to 400 nm , respectively.

FIG. 4 shows the experimental device used to carry out the contact resistance measurements indicated above.

On the contact 1 according to the invention, consisting of a brass substrate 2 coated with a layer of lubricated nickel 3 produced in the manner indicated above, a golden ball 4 is applied with a normal force F, variable and controlled. A DC voltage source 5 and an electrometer 6 are used, these two devices being connected by a data and control bus to an appropriate computer system 7.

The various resistances of the equipment (electrometer, cable, etc.) are taken into account for the calculation of the effective voltage drop Vc at the contact.

The measurements are carried out for support forces between 0.3 and 2 N, which give very linear characteristics (I _c , V _c ) making it possible to deduce a characteristic value of R _c .

FIG. 5 also shows the characteristics R _c = f (F) obtained respectively: for a contact according to the invention (referenced curves), for a conventional non-lubricated gold contact (referenced curves) or lubricated (referenced curve) and for a bare nickel contact (referenced curves).

These characteristics have been noted for a contact between a gold-plated nickel-plated plane and a Cu-Be ball of de 3.2 mm of final coating and finish. corresponding to the four cases considered, with a constant and imposed current of 10 mA.

We see that we achieve, thanks to the teachings of the invention, electrical performance quite comparable to that provided by gold contacts, but of course at a much lower cost.

Example II

In this second example, a PFAE is no longer used as a lubricant but a non-fluorinated polymer such as a PPE, that is to say a poly (phenyl ether).

Like PFAEs, PPEs are known and used to lubricate contacts, but until now they have only been used on contacts coated with gilding, therefore exclusively for their lubricating properties.

Here again, as in the previous example, it can be seen that the PPEs hang properly on the nickel, making it possible to obtain the desired results.

Claims (10)

An electrical contact terminal for connector, characterized in that it comprises, in its contact region, a thickness of nickel essentially devoid of surface metallic coating, this thickness of nickel being coated with a layer of a lubricating agent attached to nickel. The electrical contact terminal of claim 1, wherein the lubricant is a fluoropolymer. The electrical contact terminal of claim 2, wherein the lubricant is a poly (perfluoroalkylether). The electrical contact terminal of claim 1, wherein the lubricating agent is a polyphenyl ether. The electrical contact terminal of claim 1, in which the thickness of the layer of lubricating agent is between 50 and 400 nm, for a typical minimum number of successive connection / disconnection operations between 50 and 500 operations, respectively . An electrical contact terminal comprising, in its contact region, a thickness of nickel essentially devoid of surface metal coating, characterized in that it has a lower contact resistance (Rc) at 400 mΩ and a coefficient of friction (µ) less than 0.4, these criteria being met from the first connection operation and during at least 50 successive connection / disconnection operations. The electrical contact terminal of claim 6, wherein the criteria of contact resistance and coefficient of friction are met during at least 500 successive operations of connection / disconnection. A connector, characterized in that it comprises at least one electrical contact terminal according to one of claims 1 to 7. A method of manufacturing a contact terminal according to one of claims 1 to 7, comprising the steps consisting in: (a) fabricating a contact terminal having a thickness of nickel in its contact region; (b) coating this nickel thickness with a layer of a lubricating agent; and (c) hang the lubricant on the nickel. The method of claim 9, wherein the bonding step is performed by polishing the surface of the nickel with lubricant.

Images