FR2519201A1 - PROCESS FOR THE TREATMENT OF SURFACES OF ELECTRICALLY CONNECTED ORGANS - Google Patents

Abstract

PROCESS FOR THE SURFACE TREATMENT OF ELECTRICAL CONNECTION DEVICES OF THE TYPE OF WHICH THE PART FOR CONDUCTING IS CONDUCTED IN A MATERIAL GOOD ELECTRICALLY CONDUCTIVE SUCH AS COPPER OR A COPPER ALLOY, OF ALUMINUM OR OF AN ALLOY 'ALUMINUM, SAID MATERIAL 1 PROVIDED WITH A TIN COATING OR A TIN ALLOY 4, CHARACTERIZED IN THAT IT CONSISTS OF DEPOSITING ON COATING 4 A THIN LAYER OF CHROME 5.

Description

I The present invention relates to the electrical connection interface of

  16 different electrically conductive elements between them These elements can be: electrical conductors such as cables insulated with single or multi-strand conductive core, non-insulated strands, tails of electronic components, stripped ends of insulated conductors IO of removable connection elements such as lugs, terminals. plug-in contact elements such as male / female connections with cylindrical section I 5 male / female connections with flat section printed circuit connections connections of plug-in components Said elements can be permanently connected to each other by crimping, welding, or so removable by: elastic plug-in

mechanical pressure.

  The invention applies, more particularly, to

  electrical connection elements produced in large series.

  The conduction elements are generally reali-

  sés in a material good conductor of electricity such as qciue

  copper and its alloys or aluminum and its alloys.

  As these different materials are subject to cor-

  atmospheric erosion, this can cause in extreme cases the rupture of the conductive elements (case of strands

  conductors) and in all cases an alteration of the

  its electrical with other elements by increasing the electrical resistance of the contact, it is usual to protect these materials with a metallic coating that is good conductor of

electricity.

  Among the most used coatings, we know: cadmium plating which applies mainly to aluminum alloys and steels, and which is hardly used any more than in terminal blocks, nickel plating which applies to dismountable connections, and to plug-in connections It can only be placed on finished parts when the contact zones are accessible to the chemical or electroplating bath (excluding blind holes) and when the connection elements have

not to be welded.

  Io the silvering which applies to the Inductors (strands), to the rac-

  removable ropes, plug-in connections, component shanks, component connections and sometimes to printed circuits Despite its advantages of malleability and solderability, silvering is hardly used any more than

  for high frequency connections where super conductivity

  is essential, because of the cost of the material.

  precious metals (gold, palladium) which apply to removable and pluggable connection elements, as well as to printed circuit connection areas, by deposit

on suitable underlayments.

  Such coatings are becoming more and more expensive and

  their application is, therefore, increasingly limited.

  tee. the most commonly used coatings are metallic coatings of tin or tin alloys.

  provide good protection and, thanks to their remarkable duke-

  tility find a very interesting application in the continuous processing of conductive wires and strips

  intended, after operations of 3 cutting, folding and

  mage to make removable connecting members or

  In fact, during the various operations of use.

  swims, the tin-based layer follows without cracking the diff-

  different deformations of the substrate and does not erode the tools- '

  lages, unlike other coatings.

  535 In addition to the fact that such tin-based coatings are of an acceptable cost, they have the advantage of allowing the

solder with soft solder.

  However, training has been noted in the medium to

  me, a layer of poorly conductive oxide between contacts treated with a tin-based coating so that for the passage of low intensity current or

  micro-cc 2 rant, we are forced to exert a pressure

  very high tact to cross the oxide layer This pressure

  contact ion which for micro-currents can reach several hundred grams per contact element is

  IO not very compatible with mini connector technology

  especially when these include a large number

of contact elements.

  It has also been found that the qualities of weld

  bility of such coatings decreased over time, this

  I 5 which, of course, poses a significant problem for parts

  those which sometimes risk being stored for a period

quite significant time.

  The object of the present invention is to remedy the various drawbacks mentioned above and is aimed at a method of surface treatment of electrical connection elements made of material which is a good conductor of electricity such as copper or copper alloys, aluminum. or

  aluminum alloys which have undergone an over-treatment

  face based on tin The process, object of the present in-

  vention plans to deposit on the surface coating to

  tin base a very thin layer of chromium.

  This additional treatment ensures the reduction of the tin oxides already present on the surface to be treated and increased surface protection of the whole De

  more, it ensures an increase in surface hardness

  of the contact element and, as its thickness is

  very thin, it does not modify the ductility of the protection

  tin based or its solderability.

  The invention will now be described with more

  details by referring to modes of implementation by-

  individuals, given by way of example only, and shown in the accompanying drawings in which: Figure I is a partial view, enlarged, in cross section along the arrow I in Figure 2 of a conductor treated according to the invention, Figure 2 is a perspective view of an insulated rigid conductor, stripped at its end,

  Io Figure 3 is a perspective view of a cable sou-

  ply stranded, stripped at its end, FIG. 4 is a sectional view along arrows IV of FIG. 2 or of FIG. 3,

  Figure 5 is a perspective view of a target

  l 15 ple inultibrins, stripped at its end and tinned in recovery, FIG. 6 is a sectional view along the arrows VI of FIG. 5,

  Figure 7 shows two elements of pluggable ontact

  before insertion, Figure 8 is a view in the insertion position of the contact elements of Figure 7, Figure 9 is a sectional view along arrows IX of Figure 8 showing the coupling of the two elements of Figures 7 and 8 , figure IO is a view showing a female element

  of electrical connection and a printed circuit board edge

before plugging in,

  Figure 11 is a view similar to Figure 10

  showing the two coupled elements, FIG. 12 is a partial sectional view along the lines

arrows XII of figure 11.

  In FIG. 1, there is shown an enlarged partial section of the conductor of FIG. 2 showing the detail of the protection. In 1, the substrate or base metal made of a material which is a good conductor of electricity has been shown on the surface 2 of which one has deposited a coating, according to the invention, generally identified by 3 and composed of a layer 4 of tin-based alloy to which is superimposed the very thin layer of chromium. In 2 may appear a layer of a suitable material intended to prevent the migration of certain components of the substrates 1 in the coating 4 or to promote adhesion.

coating 4.

  In Figure 2, there is shown a rigid conductor

  insulated 6 comprising a solid wire 7 housed in an insulator 8.

  IO One end of said conductor 7 is stripped and pre-

  feels a coating 3, according to the invention, deposited on a substrate 1 which is made of a material which is a good conductor of electricity

(see figure 4 and figure 1).

  In Figure 3, there is shown a flexible conductor I 5 multi-strand 8 comprising seven unitary strands 9 housed in an insulating sheath 10 One end of said conductor 8 is stripped and reveals the strands 9 which have

  each a coating 3, according to the invention, deposited on a sub-

  strat 1 made of a material that conducts electricity well (see

Figure 4 and Figure 1).

  In FIG. 4, a cross section is shown.

  dirty enlarged according to arrows IV of figures 2 and 3

  cutting the single conductor 7 of FIG. 2 or a strand

  unit 9 of FIG. 3 and showing the protection

tion 3 on substrate 1.

  In Figure 5, there is shown a flexible conductor

  multi-strand 8 seems to the conductor 8 of Figure 3

  as many unit strands 9 has housed in an iso- sheath

  lante 10 at one end of the conductor 8 a is stripped

  and lets appear the individual strands 9 to which does not

  attempt no individual coating but received overall after stripping, a tinning 11 comparable to the deposit 4 of Figure 1 and then coated with a thin layer of chromium 5

  similar to that of figure 1 (see figure 6).

  In Figures 7 and 8, a set of

  plug-in electrical contacts comprising a female element

  c le 12 and a merle element 13 of cylindrical shape, one of the ends of which comprises lugs 14 for fixing a flexible conductor 15 The male element 13 is produced from

  a strip of material which is a good conductor of electricity,

  said strip being coated, on its two faces, with protection 3 composed of a layer of tin 4 on the one hand, and of a

  thin layer of chromium 5 on the other hand (see figure 1)

  ment female 12 is also produced from a strip

  of good electrically conductive material which has been pre-

  Io alably coated on at least its inner face, with protection 3 of FIG. 1 For the male element 13 as for the female element 12, the final shape can be

  obtained by cutting, rolling and stamping the sheet

  the metallic previously treated.

  I 5 -The female element 12 has at its free end a tubular part of substantially cylindrical shape in which are made three oblong stampings 17 parallel to the axis of the cylinder and whose convexities are turned towards the inside of said cylinder in order to cooperate

  with the cylindrical surface of the male element 13 The pressure

  contact is ensured by a slot 16 which allows the tubular part to open elastically over any

  its length during the introduction of the male element.

  The electrical contact is ensured by the stampings 17 of the female element and the cylindrical part of the male element which have received the same treatment 3 composed of a deposit

  4 based on tin coated with a thin layer 5 of chromium.

  In Figures 10 and 11, there is shown respectively-

  in the separation position and then in the coupling position-

  ment, on the one hand, a female contact element 18 connected to a conductor I 5 a by crimping claws 19 and 20 and, on the other hand, the edge of a printed circuit board

  single sided for example 2 I coated with a conductive track

  trice 2 'and which acts as a male contact element.

  The printed circuit is produced from a plate 23 of insulating material comprising on one of its faces the conductive track 22 generally made of copper on which the coating 3 of FIG. 1 has been deposited, composed of an alloy layer coated tin 4

a thin layer of chromium 5.

  The female contact element 18 of a known type is obtained from a strip of material which is a good conductor of electricity on which the coating 3 of FIG. 1 has been deposited on both sides before machining, as for

  element 13 of FIGS. 7, 8 and 9.

  IO The plug-in part of the element 18 consists of two branches 24 and 25 substantially symmetrical with respect to the coupling plane, the free ends 26 and 27 of which are folded backwards, forming convexities 28 and 29 turned one opposite each other The elasticity I 5 of the arms 24 and 25 and the folded free ends 26 and 27 ensuring at the contact points 28 and

  29 and after introduction of the printed circuit 21 a pres-

  sion P (Figure 12) on the side of the conductive track 22 equi-

  released by a back pressure P 'on the side of the iso-

lante of said printed circuit 21.

  The surface treatment according to the invention is very

  advantageous in that it allows first of all to keep the duke

  tility of the coating based on tin and thereby authorizes the production of contact elements by cutting, bending,

  bending, stamping from a metal strip pre-

  alably treated on one or both sides, so

  therefore continuous, under economic conditions.

  In some cases it is desirable to perform

  treatment before the organ is made in order to

  provide a uniform coating on areas that would be inaccessible if the treatment were carried out on the finished parts. It also makes it possible to considerably reduce the degradation over time of the electrical performance of the electrical connection members thus protected at room temperature, in heat z (he , ern humid heat, foggy

  saline as well as in an industrial atmosphere.

  From tests carried out, it was found that the dimi-

  significant nution of the surface oxidation allows the use of electrical connection members treated according to the invention in connections intended for the passage of microcurrent (of the order of 10 microeampers) with a contact pressure very reduced compared to that required for the same result with a known coating based on tin. Such a coating can be applied perfectly:

  even to miniature connectors even if these have

IO are trying a lot of contact.

  In view of the results obtained with the invention, the surface treatment can be generalized to a wide variety of different electrical connection members, covering in particular current ranges between the

  I 5 micro-amperes and several tens of amps.

  Tests have also been carried out, it has been determined that the electrical connection members coated with a thin layer

  of chromium could remain stored for a significant period of time

  as long as their weldability is not significantly modified over time This particular interest of the invention also applies to the electrical conductors of FIGS. 2, 3 and 4 treated continuously over their entire length, to the electrical conductors of FIGS. 5 and 6 treated in taken up on their stripped ends, the soldering tabs of electronic components, the tinned solder pads of printed circuits, 9 e which eliminates the obligation to protect them by

depositing a storage varnish.

  The thin layer of chromium can be deposited by any

  mode-appropriate, for example by a galvanoplastic process

  chemical or vacuum evaporation.

  The choice of the process to be used, i.e. the continuous processing of a wire, a blank tape, a

  pre-cut strip, bulk processing of finished parts

  born or in resumption of part, parts, will depend on the

  nature of the electrical connection member to be treated.

  ien heard, the invention is not limited to the modes of Implementation which have just been said, we can make many modifications of details

  without departing from the framework of the invention.

IO

R E V E M? D I C A T I O N

  Process for the surface treatment of electrical connection members of the type, the part of which is intended for

  ensure conduction is made of a good material

  conductor of electricity such as copper, or a copper alloy, aluminum or an aluminum alloy, said: 1 material being provided with a coating of tin or a tin alloy characterized in what it is to file

  on this coating a very thin layer of chrome.