EP0673446B1 - Method for continuously producing an electrical conductor made of copper-plated and tin-plated aluminium, and conductor so produced - Google Patents

Abstract

PCT No. PCT/FR93/01148 Sec. 371 Date Jun. 1, 1995 Sec. 102(e) Date Jun. 1, 1995 PCT Filed Nov. 22, 1993 PCT Pub. No. WO94/13866 PCT Pub. Date Jun. 23, 1994Process for continuous manufacture of an electrical conductor consisting of an at least partially aluminium-based central core coated by continuous electrodeposition with at least one metal layer, including pretreatment of the surface of the core, characterized in that the following are subsequently performed successively on the core, a) an electrochemical deposition of copper in an aqueous bath maintained at a temperature of between 20 DEG C. and 60 DEG C., containing KCN, CuCN, K2CO3 and KNaC4H4O6 with a current intensity of between 1 and 10 A/dm2; b) rinsing at ambient temperature; c) an electrochemical deposition of tin in an aqueous bath maintained at a temperature of between 20 DEG C. and 60 DEG C., containing essentially tin dissolved in methanesulphonic acid and, optionally, additives, with a current intensity of between 1 and 100 A/dm2; d) rinsing with water at 60 DEG C.

Description

The present invention relates to a continuous manufacturing process of an electrical conductor at least partially based on aluminum coated with copper and tin.

The invention also relates to an electrical conductor consisting of a central core based on aluminum comprising a solderable and oxidation-resistant metallic coating consisting of a layer of copper and a layer of tin.

Aluminum is a metal that offers a good compromise between conductivity, mechanical strength, mass and cost.

The use of coated aluminum conductors to manufacture electrical cables is increasingly common in the aeronautical and space industries.

However, the development of aluminum conductors for cables of small cross section is more difficult and requires solving a number of technical problems. The major difficulty stems from the fact that the central aluminum core must be coated in order to be resistant to oxidation and solderable to tin alloys. However, the deposition on the aluminum of a metallic layer either by electrolytic means or by immersion in hot bath proves to be very difficult because of two phenomena occurring during surface treatments.

The first concerns the chemical displacement of metals on aluminum because the latter has a very negative electrochemical potential, vis-à-vis most metals.

The second is the spontaneous formation of an oxide film on the aluminum surface, even at room temperature.

These two phenomena prevent the good adhesion of the metal layer on the aluminum substrate.

Consequently, during soft soldering operations with tin alloys at temperatures between 210 ° C and 250 ° C, the metal layer which binds with the filler metal in the molten state tends to detach from the substrate thus causing a rupture of the welded junction.

Huge work has been done to overcome the difficulties encountered in electroplating on an aluminum wire. Certain special treatment methods have been established which make it possible to deposit, for example, a nickel coating. However, the nickel-plated aluminum wire has a fairly poor solderability at the tin solders, which constitutes a significant handicap for its electrical application. More recently, research carried out in this field has made it possible to electroplate silver on an aluminum wire, which gives it good solderability.

The article "Electroplating on Aluminum Wire" pages 67-71 of Transactions of the Institute of Metal Finishing - vol. 61 (1983) describes a process for electrochemically coating an aluminum wire 2.1 mm in diameter with a copper sublayer and a layer of tin.

This process consists in treating the surface of the aluminum substrate beforehand by immersion in different degreasing and bonding baths respectively.

The substrate is then coated with copper by electrodeposition in a first bath at 60 ° C. containing copper pyrophosphate and potassium pyrophosphate then the copper coating is itself coated with tin by electrodeposition in a second bath at ambient temperature containing tin sulfate and sulfuric acid.

Analysis of the tinned aluminum wire according to this process shows that the adhesion between the copper sublayer and the aluminum substrate as well as that between the tin layer and the copper sublayer are not satisfactory, which leads to problems of brazability of the driver.

The brazability of a conductive wire is expressed by its ability to be wetted by a weld in the molten state. In other words, the attachment of the filler metal in the molten state to the conductor is carried out correctly when the surface of the latter is sufficiently wetted by the said liquefied filler metal. Wettability is linked to the so-called wetting angle formed by the respective surfaces of the conductor and the meniscus of the solder at their junction point. The smaller the wetting angle, the better the wettability of the conductor in the solder used.

Thus, it has been found that the conductors coated according to the method described above did not have a satisfactory degree of wettability by the tin / lead solder alloys commonly used.

In addition, for very small aluminum substrate diameters (of the order of 0.1 mm), it turns out that the adhesion of the metal coating is even less good and that the degree of wettability of the substrate (therefore the quality of the welds) reaches a particularly low level.

The object of the present invention is to solve the above technical problems and, in particular, for very light conductors therefore of very small diameter.

• a) un dépôt électrochimique de cuivre dans un bain aqueux maintenu à une température comprise entre 20 et 60°C, contenant du KCN, CuCN, K₂CO₃ et KNaC₄H₄O₆ avec une intensité de courant comprise entre 1 et 10 A/dm²,
• b) un rinçage à température ambiante,
• c) un dépôt électrochimique d'étain dans un bain aqueux maintenu à une température comprise entre 20 et 60°C contenant essentiellement de l'étain et de l'acide méthane-sulfonique avec une intensité de courant comprise entre 1 et 100 A/dm², et
• d) un rinçage à l'eau à 60° C.

This object is achieved in accordance with the invention by means of a continuous manufacturing process of an electrical conductor consisting of a central core at least partially based on aluminum, coated by electrodeposition with at least one metallic layer comprising successively with intermediate rinses, the degreasing of the core, its pickling and the treatment of its surface to create attachment points in the form of microscopic metallic germs, characterized in that the core is then carried out successively,

• a) an electrochemical deposition of copper in an aqueous bath maintained at a temperature between 20 and 60 ° C, containing KCN, CuCN, K ₂ CO ₃ and KNaC ₄ H ₄ O ₆ with a current intensity between 1 and 10 A / dm ² ,
• b) rinsing at room temperature,
• c) an electrochemical deposit of tin in an aqueous bath maintained at a temperature of between 20 and 60 ° C. containing essentially tin and methanesulfonic acid with a current intensity of between 1 and 100 A / dm ² , and
• d) rinsing with water at 60 ° C.

• de 5 à 40 g/l de NaOH
• de 5 à 40 g/l de Na₂CO₃
• de 1 à 20 g/l de Na₃PO₄
• de 1 à 20 g/l de Na₂SiO₃
• de 2 à 35 g/l de C₆H₁₁NaO₇

et le décapage est réalisé par une immersion de 3 à 90 s dans une solution aqueuse à température ambiante contenant de 10 à 60 % en volume d'acide nitrique.According to an advantageous embodiment, degreasing is carried out by immersion for 4 to 100 s in an aqueous solution at 60 ° C comprising:

• 5 to 40 g / l NaOH
• from 5 to 40 g / l Na ₂ CO ₃
• from 1 to 20 g / l Na ₃ PO ₄
• from 1 to 20 g / l Na ₂ SiO ₃
• from 2 to 35 g / l of C ₆ H ₁₁ NaO ₇

and pickling is carried out by immersion for 3 to 90 s in an aqueous solution at room temperature containing 10 to 60% by volume of nitric acid.

In addition, the surface of the conductor is treated to create attachment points by immersion for 4 to 100 s in an aqueous solution maintained at a temperature between 30 and 60 ° C comprising from 50 to 200 ml / l of Ni (BF ₄ ) ₂ and 10 to 80 ml / l of Zn (BF ₄ ) ₂ .

• de 30 à 200 g/l de KCN
• de 20 à 100 g/l de CuCN
• de 5 à 50 g/l de K₂CO₃
• de 10 à 100 g/l de KNaC₄H₄O₆

tandis que le bain aqueux pour le dépôt électrochimique d'étain comprend :

• de 5 à 50 % d'acide méthane sulfonique
• de 1 à 100 g/l d'étain métallique
• éventuellement de 20 à 200 ml/l d'additifs.

According to advantageous characteristics, the aqueous bath for the electrochemical deposition of Cu comprises:

• from 30 to 200 g / l of KCN
• from 20 to 100 g / l of CuCN
• from 5 to 50 g / l of K ₂ CO ₃
• from 10 to 100 g / l KNaC ₄ H ₄ O ₆

while the aqueous bath for the electrochemical deposition of tin comprises:

• 5 to 50% methane sulfonic acid
• from 1 to 100 g / l of metallic tin
• optionally from 20 to 200 ml / l of additives.

Another object of the invention is an electrical conductor consisting of a central core at least partially based on aluminum comprising a solderable metallic coating and resistant to oxidation consisting of a copper sublayer and a layer tin characterized in that the wetting angle of the coated conductor is between 10 ° and 60 ° depending on the diameter of the central core and the coating thickness.

According to an advantageous characteristic, the thickness of the Cu sublayer is between 0.5 and 15 μm.

According to another characteristic, the thickness of the layer of Sn is between 0.5 and 15 μm.

According to yet another characteristic, the diameter of the central core is between 0.08 and 2.0 mm.

The conductors of the invention are particularly well suited to the production of light cables for applications in particular in the aeronautical and space fields.

• 1) dégraissage
• 2) rinçage
• 3) décapage
• 4) rinçage
• 5) préparation du substrat
• 6) rinçage
• 7) cuivrage
• 8) rinçage
• 9) étamage
• 10) rinçage.

The tinned aluminum conductor wire is therefore obtained by an electroplating process consisting in successively and continuously carrying out the following chemical and electrochemical treatments:

• 1) degreasing
• 2) rinsing
• 3) pickling
• 4) rinsing
• 5) preparation of the substrate
• 6) rinsing
• 7) copper plating
• 8) rinsing
• 9) tinning
• 10) rinsing.

Step 1) has a cleaning function by degreasing the aluminum wire leaving the wire drawing operation.

Step 3) has a double function consisting in dissolving the aluminum oxide film on the one hand and in neutralizing the possible film of liquid from the bath 1) on the aluminum wire.

The aim of step 5) is to modify the surface state of the wire by creating microscopic metallic crystal seeds. This operation makes it possible to significantly reduce the phenomenon of chemical displacement during the electrodeposition of the subsequent steps.

Step 7) makes it possible to continuously deposit a copper film electrolytically. It was chosen to create a barrier separating the aluminum substrate and the tin coating, which makes it possible to give the coated wire advantageous properties. Thus, preliminary tests have shown that this copper sublayer considerably improves the brazability of aluminum wire in tin alloy solders.

Step 9) aims to achieve the final coating of tin with a determined thickness.

Steps 7) and 9) of coating Cu and Sn are carried out with current intensities determined as a function of the thicknesses of coating sought and the running speed or the residence time of the conductor in the baths (FARADAY law).

Steps 2), 4), 6), 8) and 10) are suitable rinses making it possible to remove the liquid entrained by the running on the wire, which could cause contamination of the various treatment baths and thus reduce their duration of life.

The invention will be better understood on reading the description of the following examples:

Example 1

An aluminum wire 131050 (Aluminum PECHINEY) with a diameter of 0.51 mm was treated continuously according to the method of the invention, the composition of the baths and the treatment conditions are described below.
1) Aqueous degreasing by immersion for 28 s in a 60 ° C bath composed of: NaOH 22.2 g / l Na ₂ CO ₃ 20.0 g / l Na ₃ PO ₄ 10.0 g / l Na ₂ SiO ₃ 10.0 g / l C ₆ H ₁₁ NaO ₇ 27.8 g / l
2) Rinse with water at room temperature
3) Aqueous pickling by immersion for 20 s in a bath composed of 30% nitric acid at room temperature
4) Rinse with water at room temperature
5) aqueous treatment by immersion for 28 s in a bath of nickel fluoroborate and zinc fluoroborate at 42 ° C. Ni (BF ₄ ) 2 95 ml / l Zn (BF ₄ ) 2 30 ml / l
6) Rinse with water at room temperature
7) Aqueous copper plating at 40 ° C. with an electrolytic current of 6.8 A / dm ² by immersion for 20 s in a bath composed of KCN 80 g / l CuCN 50 g / l K ₂ CO ₃ 15 g / l KNaC ₄ H ₄ O ₆ 50 g / l
8) Rinse with water at room temperature
9) Aqueous tinning at 35 ° C with an electrolytic current of 3.0 A / dm ² by immersion for 80 s in a bath composed of the following products: Methane sulfonic acid 14% Metallic tin 50g / l Additives 100 ml / l tinning can also be carried out using a three-component bath sold by the company LEA-RONAL under the references Solderon acid - Solderon tin - Solderon "make-up".
10) Rinse with water at 60 ° C.
After the series of treatments, the yarn has a density of 2.78 g / cm ³ and a coating adhesion in accordance with international specifications. It is thus perfectly solderable with tin alloys.

Example 2.

A 5154 aluminum wire (standard NF-A-02104) with a diameter of 0.102 mm was treated according to the same method, with baths having the same compositions with the same residence times in the baths and the same intensities of electrolytic current as those from example 1 above. The wire obtained after the treatments has a density of 3.40 g / cm ³ . It has a coating adhesion and solderability similar to that of the wire of the previous example. The tests and tests carried out on the conductive shielding made with this wire in a cable coaxial have shown that the resistance to bending and thermal aging, the solderability to tin alloys and the transfer impedance are satisfactory and comparable to those obtained with a copper wire.

In order to compare the products obtained according to the process of the present invention (Examples 1 and 2) with those obtained according to the prior art with regard to solderability, a series of meniscograph measurements of the wetting angle were carried out. on conductive wires whose diameters of Aluminum wire 131050 (PECHINEY) were 0.1 mm and 2.0 mm with different thicknesses of copper and tin coatings.

The tests were carried out according to the prescriptions of "French standardization (A 89-400-Nov 91)" on the brazability measurements published by the Welding Standardization Committee (CNS) and distributed by AFNOR. This document as well as the "test method" of the Technical Union of Electricity (1983) describe methods for determining the wetting angle characteristic of the solderability of a conductor.

The principle of the measurement is as follows:

During brazing, three phases are present: the solid phase S (the part to be brazed) the liquid phase L (the molten filler alloy) and the vapor phase V (most often, air or a gas flow ). The molecular interactions between these phases taken two by two are the surface tensions called: γ _sl (solid-liquid), γ _lv . (Liquid-vapor) and γ _sv (solid-vapor). The relation existing between them and the wetting angle θ formed by the surface of the solid and that of the liquid at their intersection is given from the formula: $$\text{cos θ =}\frac{{\text{γ}}_{\text{sv}}{\text{-γ}}_{\text{sl}}}{{\text{γ}}_{\text{lv}}}$$

In the present case, the piece to be brazed S is the coated conductor according to the present invention.

The smaller the wetting angle, the better the conductability of the conductor.

Thus, still according to French standardization, it is expected that the quality of the solderability will be divided into four classes. Brazability class wetting angle ( ^• ) 1 very good 0 ≤ 30 2 good 0 ≤ 40 3 acceptable 0 ≤ 55 4 weak to bad 0> 55

The meniscograph measurements were carried out with a bath of Sn63-Pb37 filler alloy (T solidus 183 ° C - T liquidus 183 ° C) incorporated into the meniscograph and brought to 235 ° C, the wires being immersed beforehand in a non-active neutral flux characterized by its surface tension of 0.38 mN / mm for 2 seconds.

The electrolytic current intensity for the copper-plating and tin-plating baths was for all samples 1A / dm ² .

The steps for preparing the surface (steps 1, 3, 5) were carried out under the same conditions as for Examples 1 and 2 (same compositions of the baths, same residence times, etc.).

For the copper-plating and tinning operations, the residence times in the baths are determined by FARADAY's law from the intensity of the current and the thicknesses sought for the coating of Cu and the coating of Sn (these thicknesses are given in table I below). TABLE I sample number Al wire diameter (mm) Cu thickness (µm) Thickness of Sn (µm) Wetting angle (degree °) densities (g / cm ³ ) prior art 30 2.0 0.5 0.2 134 2.71 31 2.0 2.0 1.0 134 2.73 32 2.0 2.0 10.0 134 2.81 33 0.1 1.0 2.0 149 3.25 invention 34 2.0 0.5 0.2 57 2.71 35 2.0 2.0 1.0 44 2.73 36 2.0 2.0 10.0 30 2.81 37 0.1 1.0 2.0 46 3.25 38 2.0 5.0 10.0 18 2.85 39 2.0 5.0 15.0 10 2.89

Claims (11)

1. Process for continuous manufacture of an electrical conductor consisting of an at least partially aluminium-based central core coated by continuous electrodeposition with at least one metal layer, including successively with intermediate rinsings the degreasing of the core, its pickling and the treatment of its surface in order to create thereon bonding points in the form of microscopic metal seeds, characterized in that the following are subsequently performed successively on the core,

   a) an electrochemical deposition of copper in an aqueous bath maintained at a temperature of between 20°C and 60°C, containing KCN, CuCN, K₂CO₃ and KNaC₄H₄O₆ with a current intensity of between 1 and 10 A/dm²,

   b) rinsing at ambient temperature,

   c) an electrochemical deposition of tin in an aqueous bath maintained at a temperature of between 20°C and 60°C, containing essentially tin and methanesulphonic acid and, optionally, additives, with a current intensity of between 1 and 100 A/dm², and

   d) rinsing with water at 60°C.
2. Process according to Claim 1, characterized in that the degreasing is performed by an immersion for 4 to 100 s in an aqueous solution at 60°C including:

   from 5 to 40 g/l of NaOH

   from 4 to 40 g/l of Na₂CO₃

   from 1 to 20 g/l of Na₃PO₄

   from 1 to 20 g/l of Na₂SiO₃

   from 2 to 35 g/l of C₆H₁₁NaO₇.
3. Process according to one of Claims 1 or 2, characterized in that the pickling is performed by an immersion for 3 to 90 s in an aqueous solution at ambient temperature, containing from 10 to 60 % by volume of nitric acid.
4. Process according to one of the preceding claims, characterized in that the surface treatment of the conductor in order to create bonding points is performed by an immersion for 4 to 100 s in an aqueous solution maintained at a temperature of between 30°C and 60°C, including from 50 to 200 ml/l of nickel fluoroborate and from 10 to 80 ml/l of zinc fluoroborate.
5. Process according to one of the preceding claims, characterized in that the aqueous bath for the electrochemical deposition of Cu includes:

   from 30 to 200 g/l of KCN

   from 20 to 100 g/l of CuCN

   from 5 to 50 g/l of K₂CO₃

   from 10 to 100 g/l of KNaC₄H₄O₆.
6. Process according to one of the preceding claims, characterized in that the aqueous bath for the electrochemical deposition of tin includes from 5 to 50 % by volume of methanesulphonic acid in which are dissolved 1 to 100 g/l of tin and, optionally, additives.
7. Electrical conductor consisting of an at least partially aluminium-based central core comprising a metal coating which is resistant to oxidation and brazable, made up of an underlayer of copper and a layer of tin, characterized in that the wetting angle of the coated conductor is between 10 and 60°, the wetting angle being determined according to the specifications of French standardization (A 89-400-Nov 91) for brazability measurements, published by the Comité de Normalisation de la Soudure (CNS) [Committee for Standardization of Welding] and distributed by the AFNOR.
8. Conductor according to Claim 7, characterized in that the thickness of the Cu underlayer is between 0.5 and 15 µm.
9. Conductor according to one of Claims 7 or 8, characterized in that the thickness of the Sn layer is between 0.5 and 15 µm.
10. Conductor according to one of Claims 7 to 9, characterized in that the diameter of the central core is between 0.08 and 2.0 mm.
11. Use of the electrical conductor according to one of Claims 7 to 10 for the production of cables intended for aeronautics and space applications.

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