CH668660A5 - ELECTRIC CONDUCTOR COATED WITH AN ADHERENT INSULATING LAYER RESISTANT TO HIGH TEMPERATURES. - Google Patents

Description

DESCRIPTION

The present invention relates to electrical conductors operating at high temperature and, more particularly, insulated copper wires intended for temeperatures at which the layers of usual organic insulating materials are destroyed by pyrolysis and thermal degradation. The invention also relates to a process for obtaining such insulated copper conductors resistant to high temperatures.

To insulate copper wires that have to withstand high temperatures, it has been proposed to use mineral refractory coatings such as BN, AIN, AI2O3, SÌO2, etc. However, the coatings of such minerals on copper (regardless of the deposition technique used) exhibit poor adhesion to the substrate and tend to crumble or come off during handling of the wire. We have therefore sought to remedy these defects by adding an intermediate anchoring layer between the copper substrate and the refractory lining. The following documents describe such a solution.

Document DE-A-2,500,160 (GOULD) describes a bonding layer deposited on a Cu substrate and obtained by galvanic means by adding a nitrate to a copper bath. This results in the formation, on the base metal, of Cu nodules which improve the adhesion between the latter and a terminal insulating layer, the latter possibly being made of synthetic resin (applications to printed circuits).

The document US-A-3,564,565 (TEXAS INST) describes a deposit of BN on Cu. The base metal is made adhesive by application of an intermediate layer (deposited by any means) of a metal such as Va, Cr, Mn, Fe, Ni, Si, Ge, Ag, Au, Al, P, Co, As, Sb, Ti, Zn, Ni, Mo, Ru, Rh, Pd, Ta, W, Re, Os, Ir, Pt and partial diffusion of this metal in the substrate.

Document GB-A-2 140 460 (DOWTY) describes the deposition of an insulating layer of Al203 or SÌO2 on the Cu. The intermediate anchoring layer consists of 1 (im of Fe or Mo deposited by spraying or in the vapor phase.

Document DE-A-3 417 387 describes the deposition of a vitreous insulating coating on metals such as Cu, Mo, W, etc. 20 Applications: microcircuits. Insulating layer: AI2O3 - BaO -B2O3 - SÌO2 obtained by melting at temperature exceeding 800 ° C. Intermediate anchoring layer: Neither electrolytic or "electro-less".

The document Z. Werkstofftechn. (1973), 4 (2), 72-6 (SIE-25 MEMS) describes the deposition of an insulating layer of mica on the Cu. This operation is carried out anodically in an aqueous suspension of mica particles.

Document FR-A-2 102 630 describes a connection technique between an insulator (glass, quartz, ceramic) and a metal (Cu, 30 Ni, Ag, Au, Pt). A composition containing a metal and a stripper is sprayed onto the insulator. It is heated to 500-900 ° to expel volatile matter and the metal layer is thickened galvanically.

DE-A-3 525 416 (KOLLMORGEN) describes (inter alia) the electrophoretic deposition of a resin layer containing particles (not exceeding 5 | x) of a "solid filler". The presence of the latter improves the adhesion of a Cu film deposited subsequently on the resin.

Although the techniques mentioned above are of interest, they are not exempt from certain defects linked, in particular, to the presence of organic material in the anchoring layer (this material being capable of producing undesirable effects by decomposition at high temperature), or that of metals other than copper. Foreign metals 45 indeed diffuse into copper at the temperatures of use of the insulated conductor and gradually modify its conductive properties.

Consequently, a new type of conductor isolated by a well-adherent refractory layer was sought, which led to the conductor described in claim 1. For the preparation of this conductor, the process described in claim 8 was used and, from preferably in claim 9.

The invention is illustrated by the attached drawing.

Figure 1 shows, in schematic section, a conduc-tor according to the invention.

FIG. 2 constitutes a variant of the conductor of FIG. 1.

FIG. 3 schematically represents a device for carrying out the method according to the invention.

mi Figure 4 shows a plan view of the same device.

The conductor illustrated in FIG. 1 comprises a copper core or substrate 1 on which an anchor layer 2 of electrolytic copper 2 is successively deposited containing, in dispersion, mineral particles 3 and a refractory layer 4. r, 5 It will be noted that a proportion of these particles emerges from the copper layer; it is likely that the good adhesion of the mineral layer 4 to the anchoring layer is due to the presence of these emerging particles which confer on the surface of this

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668,660

anchor layer has a rough texture and perhaps the fact that a chemical bond, by oxygen bridges, forms between the insulating layer and said mineral particles embedded in the bonding layer.

It will also be noted that in the drawing, the thickness of the electrolytic copper layer exceeds the average size of the particles, a part of these floating in some sort on the copper layer. In fact, the thickness of the anchoring layer can be arbitrary and can correspond to several diameters of particles (for example from 2 to 20 diameters), these being dispersed within the metal of this anchoring layer. However, such an arrangement is not necessary and the variant according to FIG. 2 is also possible. According to this variant, the thickness of the electrolytic layer 2 is less than the useful size of the particles 2, the latter being, in fact, trapped in the copper layer and exceeding the level of the latter. It should be noted that a thick anchor layer rich in mineral particles (several particle diameters) makes it possible to absorb surface tensions due to the differences in thermal expansion between the copper and the terminal insulating mineral coating. However, an excessively thick anchor layer can be disadvantageous for reasons of bulk and changes in conductivity.

The volume proportion of the particles in the anchoring layer is not critical. It is however necessary that the proportion of the particles is sufficient to ensure a suitable adhesion of the insulating mineral layer. By the way,

this proportion must not be excessive so as not to compromise the adhesion of the anchoring layer to the copper core. Preferably it is preferred that the proportion of the particles in the electrolytic copper is between 1 and 100%, that is to say between 1 volume and 100 volumes of particles per 100 volumes of copper.

The mineral particles can be chosen from materials such as silica, alumina and boron nitride; their size is preferably between 0.1 and 10 µm.

To obtain the conductor according to the invention, the intermediate layer is deposited, preferably galvanically by means of an electrolytic copper bath containing the mineral particles in suspension. The nature of the copper bath is not critical and it is possible to use both an acid and an alkaline bath (with cyanide for example). However, acid baths with copper sulphate are preferred according to the usual practice in industrial electroplating, this bath being able, for the deposition of the anchoring layer, to contain from 0.1 to 20% of mineral particles in suspension. Preferably, the intermediate layer is plated at room temperature under 0.5 to 5 A / dm2 for a period of a few seconds to a few minutes, for example 10 sec. at 3 min. Under these conditions, an intermediate layer is obtained, the copper of which has a thickness of between a few hundredths of a µm and 5-100 µm. Of course, the thickness of this anchoring layer will be chosen according to the needs; it will preferably be as thin as possible in the case of small diameter conductors (for example wires from 0.05 to 0.5 mm); it may be thicker for larger conductors.

As for the insulating mineral layer, it will be produced according to the usual criteria and according to needs according to the requirements to which the electrical circuits produced by means of these conductors will be subjected. Thus, their thickness will vary depending, for example, on the electrical voltage applied to the wire as well as on the capacitive parameters.

To deposit the insulating layer, the usual techniques for coating mineral layers can be used: CVD (chemical deposition in gas phase), spray deposition, plasma deposition, or dipping deposition.

As regards the CVD technique, it is possible, for example for BN deposits, to react in gaseous form at high temperature a boron halide with ammonia according to the usual means; for SÌO2, SÌCI4 can be reacted with water vapor.

With regard to the “dip” technique, the wire covered with its anchoring layer is brought into contact with a solution containing precursor ingredients which, after adhesion to the wire, drying and pyrolysis, provide the desired coating. Thus for SÌO2, the wire can be dipped in a gel-reliable solution (by water) of alkyl silicate, this solution providing by hydrolysis a polysiloxane coating which, by drying then pyrolysis is converted into adherent amorphous silica. For an alkali silicate coating, the wire is dipped in a solution of silica in caustic soda then, after removing the wire from this solution, the coating is dried and cured by heating in air at temperatures of l '' from 300 to 400 ° C.

The following examples illustrate the invention.

Example 1

In a metal container 5 (copper or platinum-plated titanium) such as that shown in FIG. 3, a support 6 has been arranged vertically in insulating material (glass or plastic), this support being arranged (as illustrated in the drawing) to support, stretched by its ends, a portion 7 of bare copper wire of 0.5 mm diameter.

An aqueous electrolytic polishing bath containing H3PO4 600 g was introduced into the container; H2SO4 100 g; glycerin 100 g and H2O 200 g, and electrolysis was carried out for 1 min. at 70 ° C under 100 A / dm2, the wire being connected by its end 8 to the anode of a direct current generator and the container to the corresponding cathode.

Support 6 was removed from the bath with wire 7 and rinsed successively with H2O, distilled H2O and alcohol. Then an electrolytic copper bath containing 209 g / l of CUSO4 and 52 g / l of H2SO4 containing 6.4 g / l of SÌO2 (AERO-SIL, DEGUSSA) in particles of approximately 1 μm was placed in the container. bath was stirred magnetically or by means of a gas introduced into the bottom of the container by means of a tube not shown.

The support 6 was briefly soaked in 5% aqueous H2SO4 in order to activate the copper in the wire 7 and it was introduced into the container 5, after which the electrolysis was carried out for 1 min. at 25 ° C under 3 A / dm2.

The support was then removed and the wire rinsed with distilled water; its surface had a finely rough texture. This wire was soaked in an aqueous solution containing 5 g of SÌO2 / Aerosil), 40 g H2O and 55 g of sodium silicate (Na20 • 3SÌO2) and it was removed at a speed of 50 cm / min. Then the wire was dried lh at 50 ° C, lh at 120 ° C and lh at 400 ° C. There was thus obtained an insulating silicate coating resistant to temperatures from 400 to 600 ° C. and well adherent to the surface of the wire.

Exempt 2 and 3

The operations described in Example 1 were identically repeated with, as a modification, replacing the silica of the copper bath with identical quantities of:

AI2O3 (1-5 pm) = Example 2

Hexagonal BN (~ 1 pm) = Example 3

These samples were then subjected to the treatment leading to the formation of the silicate insulating layer as in Example 1. Similar results were obtained.

Example 4

The procedure was as in the previous examples and coated by dipping with a potassium silicate solution (AREMCO CERAMABOND-571) of samples rendered adhesive by intermediate layers containing either SÌO2,

either AI2O3 or BN. The treatments recommended for final deposit by AREMCO PRODUCTS INC. Ossining, N.Y. 10562, that is to say drying for one hour in air, followed by heating for 2 hours at 93 ° C. were carried out. The adhesion of these insulating layers has been recognized as excellent.

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Claims (12)

668,660 1. Insulated copper electrical conductor for high temperatures comprising a copper core coated with a refractory mineral insulating layer, characterized in that it comprises, between the core and the insulating layer, an anchoring film constituted by a mixture of electrolytic copper and fine refractory mineral particles. 2. Conductor according to claim 1, characterized in that the anchoring layer is rough, at least some of the particles emerging from the thickness of the electrolytic copper. 2 3. Conductor according to claim 1, characterized in that the proportion by volume of the particles relative to that of the electrolytic Cu is between 1 and 100%. 4. Conductor according to claim 2, characterized in that the particle size exceeds the thickness of the electrolytic Cu. 5. Conductor according to claim 2, characterized in that the particle size is between 0.1 and 10 p.m. 6. Conductor according to claim 2, characterized in that the mineral particles are chosen from SÌO2, AI2O3, TÌO2 and BN. 7. Conductor according to claim 1, characterized in that the material of the refractory insulating layer is chosen from BN, AIN, AI2O3, a suitable silicate or phosphate. 8. A method for obtaining an insulated copper electrical conductor for high temperatures according to claim 1, characterized in that, successively, deposited on a copper core, an intermediate anchoring layer of electrolytic copper containing, in dispersion, mineral particles, then a layer of a refractory mineral. 9. Method according to claim 8, characterized in that, for the intermediate layer, a galvanic Cu bath is used containing, in suspension, said mineral particles. 10. Method according to claim 9, characterized in that an acid or alkaline bath is used containing from 0.1 to 20% by weight of mineral particles. 11. Method according to claim 10, characterized in that a copper sulphate bath is used and that the operation is carried out at 0.5 to 5 A / dm2 for 10 seconds to 3 minutes at room temperature. 12. Method according to claim 10, characterized in that after deposition of the intermediate layer, one proceeds to the deposition of the insulating layer by a technique chosen from chemical vapor deposition, or soaking in a solution containing reagents precursors of the components of the mineral layer, this soaking being followed by drying and then pyrolysis.