EP1304022A1 - Method for making a circuitry comprising conductive tracks, chips and micro-vias and use of same for producing printed circuits and multilayer modules with high density of integration - Google Patents

Abstract

The invention concerns a method for making a circuitry comprising conductive tracks, chips and micro-vias, at the top surface of a dielectric (303) consisting of a polymer matrix, a compound capable of inducing subsequent metallization and, if required one or several non-conductive and inert fillers, said dielectric (303) covering a level of circuitry (302) or metallized layer, which comprises steps which consist in: a) perforating right through said dielectric (303) without perforating the subjacent metallized layer or the subjacent level of circuitry (302), so as to form one or several micro-vias (304) at desired sites; b) forming, by metallization, metal tracks (312), chips (313) and micro-vias (311) at the surface of the dielectric (314) and of the micro-vias (304), while providing selective protection by depositing a protective layer.

Description

 Method for producing circuitry comprising conductive tracks, pellets and microwires and use of this method for producing printed circuits and multilayer modules with high integration density.

The invention relates to an improved method for producing interconnection circuitry with a high integration density comprising conductive tracks, pads and micro-crossings.

In the context of the invention, the term “micro crossings” means the blind micro holes passing right through the thickness of a dielectric layer. Microtraverses are commonly known as microvias in the art.

In the field of electronics, there is a trend towards optimal miniaturization of products as well as an increase in performance in terms of speed. These trends are accentuated by the growing use of surface connection components such as BGA / CGA, CSP or other Flip Chip.

Integration densification is desirable in three dimensions: both in an axial direction by successive stacking of increasingly thin dielectric / copper layers to obtain a multilayer, than in the plane perpendicular to this direction by bringing tracks together. and increasingly fine pastilles. The process of the invention meets these requirements by ensuring the development of "fine line" circuitry characterized by widths of tracks and interpenetrators less than 100 μm and diameters of holes or crossings less than 100 μm.

This process also ensures excellent adhesion of the metal layers to the dielectric substrate and limits the phenomena of under-etching, that is to say it makes it possible to avoid non-uniform etching at the level of microtravers.

The method of the invention is also economically advantageous insofar as it allows a simplification of the overall procedure for metallization of the bushings, pads and tracks by reducing the number of steps.

According to a first of its aspects, the invention provides a method of forming and metallizing blind or microtrossed holes in a dielectric covering a first level of circuitry or a first metallized layer, without deterioration of said first level of circuitry or of said first layer Metallic.

A conventional state-of-the-art method consists in implementing the succession of the following different stages: - etching and possibly oxidizing a metallized layer carried by a dielectric

(RCC mounting); - pierce one or more micro-crossings in the dielectric at the places where the metallic layer has been etched and oxidized;

- carry out a surface treatment by acid pickling (or de-icing) by oxidizing process to promote the subsequent attachment of metal particles; - Sensitize and activate the resulting surface, the sensitization generally being carried out by immersion in an acid solution of stannous salt; and the activation can be carried out by soaking in an aqueous solution of a palladium salt;

- Metallizing electrochemically without current the resulting activated surface, the microtravers also being metallized during this operation; - optionally reinforcing the metal layer obtained by subsequent metallization by electrolytic means;

- proceed to drying and brushing the resulting surface;

- coat the part constituting the interconnection circuitry with a protective layer; then - etch the unprotected metal.

EP 82 094 also describes a simplified method of metallization of plastic substrates according to which an electrically insulating substrate is first produced by the association of a polymer resin and copper oxide particles, then reduced to at least part of the cuprous oxide present in said metallic copper resin, then the desired metallic layer is then deposited, said process being in particular characterized in that the reduction in metallic copper is carried out by the action of borohydride and in this that it does not include an activation step or an awareness step.

The manufacture of interconnection circuitry from the metallized element obtained by implementing the method of EP 82094 would involve steps similar to those described above, with a view in particular to the formation of blind crossings. Surprisingly, the inventors have developed a process allowing the rapid formation of interconnections (tracks, pads and microtraverses) on the surface of a dielectric in order to prepare integrated circuits, printed circuits and multilayer modules with high density of integration. This process, in addition to its simplicity of implementation, has the advantages of a solid anchoring of copper on the surface of the dielectric and of an optimal miniaturization of microtravers.

More specifically, the method of the invention makes it possible to develop an interconnection circuit comprising tracks, pellets and conductive microt crossings, at the upper surface of a dielectric consisting of a polymer matrix, of a compound capable of inducing a subsequent metallization and, where appropriate, one or more other non-conductive and inert charges, said dielectric covering a level of circuitry or a metallized layer, by implementing the steps consisting in:

A) - pierce right through said dielectric without piercing the underlying metallized layer or the level of underlying circuitry, so as to form one or more micro-crossings at the desired locations;

B) forming, by metallization, metal tracks, pellets, and micro-crossings on the surface of the dielectric and micro-crossings, with the implementation of selective protection by depositing a protective layer.

The circuitry is obtained by stacking and drilling layers and / or deposits of materials of different natures, on defined parts. Metallic tracks, pellets and microtracks are thus separated, separated in places and supported by layers of dielectric material.

The tracks, pads and microtraverses form an interconnection circuit. The tracks are parts of circuitry positioned on the surface of a dielectric material. They are generally in the form of lines of reduced thickness.

The circuitry according to the invention can include several levels of circuitry.

Each level of circuitry corresponds to a set of tracks on the surface of a dielectric material. The circuitry levels are therefore separated by a layer of dielectric material, with in places metallic connections between the levels. These metallic connections between two or more levels are called micro-crossings. The pellets correspond to an enlargement of a metal deposit in the areas where the microtravers emerge. Such structures are known to those skilled in the art.

According to the invention, the tracks, pellets and microtraverses are formed on the upper surface of a dielectric which comprises a compound capable of inducing subsequent metallization. The dielectric covers a circuit level (a lower circuit level) or a metallized layer. The dielectric can be placed on the circuit level or on the metallized layer in liquid form, undergoing a subsequent solidification. It can also be applied as a solid laminate product. In the latter case, it is possible to use a two-layer laminated product comprising for one side a layer of said dielectric comprising the compound capable of inducing a subsequent metallization and for the other side a layer of metal (RCC). The laminated product is applied in two layers on the circuit level or the metallized layer so that the face comprising the compound capable of inducing subsequent metallization covers the level of circuitry or the metallized layer, and the metal layer is removed from the rolled product, for example by etching. A dielectric surface is thus obtained which makes the peeling force of the metal deposits (tracks, pads) which will be formed thereon particularly important. This technique is often called "full etching". The level of circuitry covered by the dielectric can itself be produced by a method according to the invention. It can also be produced by another method. It may for example be a printed circuit on one or more levels, on a rigid or flexible support, possibly with conductive crossings. For the support, it may for example be an injected insulating material or a conventional composite material in the field of printed circuits. Examples are epoxy / glass fiber-based supports. It may be a dielectric material comprising a sheet of nonwoven fibers or a paper, impregnated with dielectric resin. The presence of the fiber web or paper ensures good uniformity of the thermal expansion coefficients (CTE). In a particularly advantageous manner, the support is a sheet made up of nonwoven aramid fibers (commercial aromatic polyamide) pre-impregnated with an epoxy resin, a polyimide resin or a mixture of these resins. More preferably, these aramid fibers (which are preferably meta-aramid, para-aramid fibers or a mixture of such fibers) are pre-impregnated with functionalized polyimide-amide resin (with chemical units which can be crosslinked when hot). This functionalization can be obtained with double bonds or maleimide groups as defined in patent EP 0 336 856 or US 4 927 900. Advantageously, the sheet comprises from 35 to 60% by weight of dielectric resin, preferably from 44 to 55 % by weight, better still from 40 to 50% by weight, for example 47% by weight. For example, the thickness of the sheet varies between 10 and 70 μm, preferably between 15 and 50 μm, better still between 20 and 40 μm.

Its grammage generally varies between 10 and 50 g / m ² , better still between 15 and 40 g / m ² .

It is specified that the circuitry obtained by the method according to the invention can be carried out on one or two faces.

During step A) the dielectric is drilled right through so as to form one or more micro-crossings at the desired locations, without piercing the level of underlying circuitry or the underlying metallized layer. The micro-crossings are subsequently metallized in order to establish connections through the dielectric.

The drilling can be carried out in a conventional manner, by plasma or laser, the latter technique being clearly preferred insofar as it leads to Significantly smaller microstream diameters and allowing significantly higher drilling rates.

Among the lasers that can be used, mention may be made of YAG lasers, C0 ₂ , combined lasers

YAG-C0 ₂ or the Excimer lasers. Those skilled in the art will easily be able to select the appropriate laser according to the dielectric to be drilled. Particular attention will be paid to the final drilling phase, it being understood that the underlying metallized layer or the level of underlying circuitry must remain intact.

The C0 ₂ laser which operates at wavelengths from 9300 nm to 10600 nm is particularly preferred for the implementation of step A) insofar as it allows selective drilling of the dielectric without touching the metallic layer under adjacent and this without any additional adjustment being necessary, the metal layer not being attacked by the laser C0 ₂ . The drilling speed of the C0 ₂ laser, greater than that of a YAG laser, also makes this drilling technique particularly advantageous. The YAG laser is more delicate in this case, since it can pierce the underlying metallized layer and requires precise control of the drilling operation in its final phase.

Preferably, the diameter of the microswitch is greater than the thickness of the dielectric.

During step B), metallic tracks, pellets and microdreams are formed by metallization on the surface of the dielectric and microdreams. For this, selective protection is implemented by depositing a protective layer. The methods of forming metallic interconnects with selective protection, in particular using photosensitive resin, are known to those skilled in the art. We cite in particular the pattern type processes, the panel type processes. For the process according to the invention, the metallization of the dielectric is made possible thanks to the compound capable of inducing a subsequent metallization, and possibly to an adequate treatment preceding the metallization, for example a treatment leading to the formation of an undercoat. suitable for being metallized. Methods of forming such an underlayer will be detailed later.

Step B) can itself include several steps. We will detail several embodiments corresponding to sequences of different stages.

As regards the compound capable of inducing a subsequent metallization, it is preferably particles of a metal oxide chosen from the oxides of Cu, Co, Cr, Cd, Ni, Pb, Sb, Sn and their mixtures . We particularly prefer the particles of cuprous oxide Cu ₂ 0. As regards the metal oxide used, it must be in the form of particles of small dimensions; the particle size is generally between 0.1 and 5 μm. The presence of metal oxide particles in the dielectric ensures a reduction in the thermal coefficient of expansion, isotropically, while promoting heat transfer.

The compound capable of inducing a subsequent metallization can also be an organometallic compound.

As regards the polymer matrix, it is a dielectric material, that is to say electrically insulating. The nature of this material is not critical according to the invention. Preferably, it is a thermoplastic polymer, a thermosetting resin or a mixture of such constituents.

As examples of thermoplastic polymers, mention may be made of polymers of polyolefinic, vinyl, polystyrene, polyamide and polyamide-imide, acrylic, polysulfone, polysulfide, polyphenylene oxide, polyacetal, polyfluorinated, polyparabanic, polyhydantoin, linear polyimide, polyalkylene oxide, linear polyurethane , saturated polyester, elastomer or a mixture of these polymers.

Suitable thermosetting resins are of the phenolic prepolymer, unsaturated polyester, epoxy, bismaleimide polyimide, reactive polyimide-amide, triazine, cyanate ester type, or a mixture of these resins. Examples of polyolefin resins are polyethylene, polypropylene and ethylene-propylene copolymers.

Vinyl resins are polyvinyl chloride, polyvinylidene chloride, ethylene-vinyl acetate copolymers.

Polystyrene resins are illustrated by polystyrene, styrene-butadiene copolymers, styrene-acrylonitrile copolymers and styrene-butadiene-acrylonitrile copolymers.

As polyamide polymer, mention may be made of polyhexamethylene adipamide (type 6-6), polyaminocaprolactam (type 6) and polyundecanamide (type 11).

As suitable acrylic polymer, use will be made, for example, of polymethyl methacrylate, linear polyurethanes and in particular polyurethanes resulting from the polymerization of hexamethylene diisocyanate with propanediol-1, 3 or butanediol-1, 4.

Saturated polyesters are for example polyethylene terephthalate or butylene glycol, fluorinated polyesters, polycarbonates, polyacetals, polyphenylene oxides, polyphenylene sulfides or thermoplastic elastomers. Phenolic resins are, for example, condensates of phenol, resorcinol, cresol or xylenol with formaldehyde or furfural. Unsaturated polyesters are the reaction products of an unsaturated dicarboxylic acid anhydride such as maleic or citraconic anhydride with a polyalkylene glycol.

By way of example of epoxy resins, mention may be made of the reaction products of chloro-1-epoxy-2,3-propane or diepoxy-1,2,3,4-butane with bis-phenol A or other phenols such as resorcinol, hydroquinone or dihydroxy-1,5-naphthalene. As elastomer, mention may be made of natural or synthetic rubbers, silicones or polyurethanes.

As suitable polyfluorides, mention may be made of polytetrafluoroethylene and poly (vinylidene fluoride).

Preferably, the polymer matrix is a thermosetting resin of the polyimide or epoxy type or alternatively a thermoplastic polymer of the polyamide-imide type.

The polymer matrix forming the dielectric may contain one or more other electrically insulating charges, completely inert under the conditions for implementing the method of the invention. They play the role of reinforcing filler and are for example formed from simple fibers, of mineral or organic nature, the length of which does not generally exceed 10 mm, such as in particular asbestos fibers, ceramic fibers or preferably glass or even they are very long reinforcement materials: threads, fabrics, non-wovens or knits.

Other reinforcing fillers consist of grains, of mineral or organic nature, such as particles of mica, molybdenum sulfide, alumina, silica, polytetrafluoroethylene or glass microbeads. The particle size of the fillers is chosen so as to be compatible with the application by deposition of the polymer matrix.

The dielectric may also include particles of calcium carbonate. These particles are capable of creating a roughness on the surface of the dielectric by dissolving by acid attack.

Preferably, the thickness of the dielectric does not exceed 100 μm. Advantageously, the dielectric layer has a thickness of between 10 and 70 μm, better still between 15 and 50 μm, for example between 20 and 40 μm.

According to a particularly preferred embodiment, the dielectric comprises, as an inert non-conductive filler, a sheet of non-woven fibers or a paper, impregnated with dielectric resin. The presence of said sheet ensures better uniformity of the thermal expansion coefficients (also called coefficient thermal expansion: CTE), without impairing the ability to ablate the dielectric by laser.

The incorporation of such a charge into the dielectric also makes it possible to reduce the thickness of the dielectric layer and therefore to further improve the miniaturization. According to a first embodiment, said load is a paper as described in FR 2 685 363 or US 5 431 782.

In a particularly advantageous manner, the filler is a sheet made up of nonwoven aramid fibers (commercial aromatic polyamide) pre-impregnated with an epoxy resin, a polyimide resin or a mixture of these resins. More preferably, these aramid fibers (which are preferably meta-aramid, para-aramid fibers or a mixture of such fibers) are pre-impregnated with functionalized polyimide-amide resin (with chemical units which can be crosslinked when hot). This functionalization can be obtained with double bonds or maleimide groups as defined in patent EP 0 336 856 or US 4 927 900. Advantageously, the sheet comprises from 35 to 60% by weight of dielectric resin, preferably from 44 to 55 % by weight, better still from 40 to 50% by weight, for example 47% by weight.

For example, the thickness of the sheet varies between 10 and 70 μm, preferably between 15 and 50 μm, better still between 20 and 40 μm.

Its grammage generally varies between 10 and 50 g / m ² , better still between 15 and 40 g / m ² .

The tracks, pellets and microtraverses are formed by metallization in step B) on all or part of the dielectric, on unprotected surfaces, either before application of the protective layer, or after application and elimination of certain parts of the latter. Metallization can be carried out electrochemically (without current) and / or electrolytically (with current). The latter route is more particularly preferred since it is faster. It can also be carried out in an acid medium, which avoids swelling of the photosensitive layers, thus improves the positioning accuracy of the various exposures and revelations, and improves the reliability and longevity of the circuitry. For metallization by electrolytic means, it is advantageous to operate at increasing intensity. The metal is preferably copper.

Electrochemical metallization (without current) is a known technique which is described in "Encyclopedia of Polymer Science and Technology, 1968, vol. 8, 658-661". Likewise, electrolytic metallization (with current) is a conventional technique also described in Encyclopedia of Polymer Science, 661-663. According to a particularly preferred embodiment of the invention, the metallization, whether electrochemical or electrolytic, is continued until a metallic layer having a thickness of at least 5 μm is obtained, preferably a thickness of between 10 and 20 μm.

Step B) advantageously comprises before metallization a step of forming a sub-layer capable of being metallized. Such an undercoat is formed over the entire surface of the dielectric, or over exposed parts of the dielectric with selective protection of the other parts. The sub-layers formed are, depending on the case, continuous or discontinuous, and lend themselves, or not, directly to metallization by electrolytic means. However, they are still suitable for metallization by electrochemical means. In this case the electrochemical deposition of metal is catalyzed by the sub-layer, and the metallization is equivalent to those using Palladium or Platinum. Two methods are preferred for the embodiment for obtaining a sub-layer capable of being metallized.

According to a first embodiment of the under layer, the compound capable of inducing a subsequent metallization is chosen from the metal oxides mentioned above, and the under layer is formed by bringing the dielectric or exposed parts of the dielectric into contact with a solution of a noble metal salt capable of being reduced by oxide particles.

During this step other layers can be brought into contact with the solution. It has no useful effect on them. A continuous sublayer of the noble metal is thus formed on the exposed surface of the first layer. The resistivity of the sub-layer is between 10 ⁶ and 10 ³ Ω / D. It is preferably less than 10 ³ Ω / D. This allows electrochemical metallization, preferably at increasing intensity. It is indicated for information that the cohesion of the sublayer is all the better the higher the concentration of oxide particles.

As solutions of preferred noble metal salts, mention is made of solutions of salts of Au, Ag, Rh, Pd, Cs, Ir, Pt, with a counterion chosen from Cl ^" , NO ^" ₃ , CH ₃ COO ^" The contacting can be carried out by soaking in the solution, spraying, passing a roller. The noble metal salt solution is generally acid, with a pH of between 0.5 and 3.5, preferably between 1, 5 and 2.5 The pH can be controlled by adding acid. This treatment in an acid medium also makes it possible to limit swelling of the resin layers which takes place in basic medium. circuitry with excellent definition and excellent flatness. that the treatment with an acid solution of noble metal salts may be preceded by rinsing with an acid solution, for example acetic acid, in the case where the first layer of photosensitive resin comprises particles of carbonate calcium. This rinsing makes it possible to increase the roughness of the surface, the calcium carbonate particles present on the surface being dissolved, and thus to improve the adhesion of the metallic deposits.

For the first mode of forming a sublayer, the metal oxide particles are preferably chosen from MnO, NiO, Cu ₂ O, SnO, and are preferably contained in the first layer up to 2.5- 90% by weight, even more preferably up to 10-30%. The preferred metal oxide is cuprous oxide Cu ₂ O. The solution advantageously comprises at least 10 ^"5 mol / L of noble metal salt, preferably between 0.0005 and 0.005 mol / L. An undercoat is obtained of continuous noble metal and thickness less than 1 μm. The undercoat obtained has excellent uniformity, which improves the quality of the connections obtained after metallization. As salts which can be used, mention may be made of AuBr ₃ (HAuBr), AuCI ₃ (HAuCI ₄ ) or Au ₂ CI ₆ , silver acetate, silver benzoate, AgBrO ₃ , AgCI0 ₄ , AgOCN, AgNO ₃ , Ag ₂ S0 ₄ , RuCI ₄ .5H ₂ 0, RhCI ₃ .H ₂ 0, Rh (NO ₃ ) ₂ .2H ₂ O, Rh ₂ (S0 ₄ ) ₃ .4H ₂ O, Pd (CH ₃ COO) ₂ , Rh ₂ (S0 ₄ ) ₃ .12H ₂ 0, Rh ₂ (S0 _{4) 3} .15H ₂ O, PdCl _2, PdCl ₂ .2H ₂ O, PdS0 ₄ SODP ₄ .2H ₂ O, Pd (CH ₃ COO) _2, OSCI ₄ OSCI ₃ OSCI ₃ .3H ₂ 0 , Osl ₄ , lrBr ₃ 4H ₂ 0, lrCI ₂ , lrCI ₄ , lrO ₂ , PtBr ₄ , H ₂ PtCI ₆ 6H2O, PtCI ₄ , PtCI ₃ , Pt (S0 ₄ ) ₂ .4H ₂ 0 or Pt (COCI ₂ ) CI ₂ , and the complexes c corresponding as NaAuCL ,, (NH ₄ ) ₂ PdCI ₄ , (NH ₄ ) ₂ PdCI ₆ , K ₂ PdCI ₆ or KAuCI ₄ . The undercoat obtained lends itself particularly well to electrolytic metallization. One can for example implement an electrolytic metallization with increasing intensity. The formation of the sub-layer in the context of the first mode, can in particular comprise the following operations:

- updating of the metal oxide particles included in the first resin layer of the dielectric. This operation is preferably carried out by alkaline attack (for example by a solution of soda or potassium hydroxide in hydroalcoholic medium) then rinsing with water, possibly under utra-sounds in order to remove the loose oxide particles, in case the dielectric contains inert charges such as calcium carbonate, creating a slight surface roughness by acid attack. This operation is preferably distinct from the operation of forming the metal underlayer.

- Formation of a continuous metallic sublayer of noble metal by contacting with an aqueous, acidic solution, of noble metal salt. AT As an indication, it is specified that the sublayer obtained is generally monoatomic, the noble metal acting as a barrier to the pursuit of the oxidation-reduction reaction. The layer is continuous because a part of the metal oxide particles releases ions by dissolution. These ions react in an aqueous medium with the noble metal salt, leading to the reduction of this metal, which is deposited thus filling the inter-particle spaces. The reaction is all the more efficient and economical as the aqueous medium of noble metal salt is more confined. For this reason, it is preferred to conduct the reaction in a thin layer, that is to say by immersion in the solution comprising the noble metal salt, and withdrawal immediately afterwards. The reaction then takes place in the layer of aqueous solution entrained with the object.

According to a second embodiment of the sublayer, the compound capable of inducing a subsequent metallization consists of metallic oxide particles chosen from the oxides of Cu, Co, Cr, Cd, Ni, Pb, Sb, and their mixing, the undercoat being obtained by subjecting all or part of the dielectric to the reducing action of an appropriate reducing agent until a metal undercoat covering in particular the microstructures is obtained, by reduction of the metal oxide particles on the exposed surface of the dielectric, the resistivity of which is between 0.01 and 10 ¹⁰ Ω / D.

For this embodiment, the proportions of the constituents of the dielectric in accordance with the present invention are preferably chosen between the following limits (expressing the percentage by weight of each of the constituents in the substrate):

- 10 to 90%, preferably 25 to 90% of metal oxide, preferably of cuprous oxide;

- from 0 to 50% of other inert filler (s) under the conditions of the reduction; and

- from 10 to 90%, preferably from 10 to 75% of polymer resin. As a variant, the dielectric consists of:

- less than 10% by weight of metal oxide, preferably of cuprous oxide; - 0 to 50% by weight of inert and non-conductive filler (s); and

- 10 to 90%, preferably 10 to 75% by weight of polymer resin.

The surface resistivity which it is preferable to achieve for the sub-layer according to the second embodiment depends on the nature of the dielectric.

When the dielectric consists of 10 to 90% by weight of metal oxide, from 0 to 50% by weight of inert and non-conductive filler (s), and from 10 to 90% by weight of resin polymer, the reduction is advantageously continued until a surface resistivity from 0.01 to 10 ³ Ω / D. The metailizations are preferably carried out in this case by electrolytic means, for example at increasing intensity.

When the dielectric is made up of less than 10% by weight of metal oxide, from 0 to 50% by weight of inert and non-conductive filler (s), and from 10 to 90% by weight of polymer resin , the reduction is advantageously continued until a surface resistivity greater than 10 ⁶ Ω / D is obtained. The metailizations are preferably carried out in this case by electrochemical means.

The presence of said continuous or discontinuous metal sublayer also catalyzes the subsequent metal deposit produced while being perfectly compatible with it.

This sublayer contributes more precisely, whether it is obtained according to the first mode or the second mode, to improve the adhesion of the subsequent metal deposit by avoiding any break in the electrical conduction at the level of the metallized bushings. Before carrying out the reduction for the formation of the underlayer, it may prove necessary to carry out a preliminary etching of the surface of the dielectric so as to make the metal oxide particles appear on the surface. This is particularly the case when all of the metal oxide particles are coated with the polymer matrix. Pickling consists either of a chemical treatment with a chemical agent capable of surface attacking the polymer matrix, or of a pickling technique using mechanical means, such as abrasion, brushing, sanding, grinding or the image.

According to a preferred embodiment of the invention, the pickling is carried out using mechanical means.

During the operation of forming the sublayer according to the second mode, when the metal oxide is a cuprous oxide, part of the copper is reduced to the CuH state, in which state the copper acts as as catalyst for the metal deposition carried out in step B). If there is an excess of CuH, the latter transforms slowly into copper metal at room temperature, with diffusion of the hydrogen towards the outside.

In the following, the presence of this transient hydride is no longer mentioned and reference is simply made to a metallic layer.

For the implementation of the reduction, a person skilled in the art can select any of the reducing agents capable of reducing the metal oxide to a metal of oxidation state 0.

Obtaining the desired resistivity values during this step will depend on the one hand on the proportions and on the nature of the metal oxide included in the matrix. polymer forming the dielectric and on the other hand, the importance of the reduction carried out, and in particular the type of reducing agent used as well as the preliminary etching step. Depending on the type of reducing agent used and on the nature of the metal oxide to be reduced, the nature of the metal layer deposited varies. According to a preferred embodiment of the invention, the reducing agent is a borohydride.

In the following, the action of borohydrides is described more precisely in the case where the metal oxide is a cuprous oxide.

By the action of a borohydride Cu ₂ 0 is reduced to metallic copper. By using this type of reducing agent, the layer formed on the surface of the dielectric is a continuous or discontinuous metallic layer of copper.

The borohydrides usable in the present invention include substituted borohydrides as well as unsubstituted borohydrides. Substituted borohydrides in which at most three hydrogen atoms of the borohydride ion have been replaced by substituents inert under the reduction conditions such as, for example, alkyl radicals, aryl radicals, alkoxy radicals, can be used. Preferably alkali borohydrides are used in which the alkaline part consists of sodium or potassium. Typical examples of suitable compounds are: sodium borohydride, potassium borohydride, sodium diethylborohydride, potassium triphenylborohydride. The reducing treatment is carried out in a simple manner by bringing the surface of the dielectric into contact with a solution of the borohydride in water or in a mixture of water and an inert polar solvent such as, for example, a lower aliphatic alcohol. Preference is given to purely borohydride solutions. The concentration of these solutions can vary within wide limits and is preferably between 0.05 and 1% (by weight of active hydrogen of the borohydride in the solution). The reducing treatment can be carried out at high temperature, however it is preferred to carry it out at a temperature close to room temperature, for example between 15 and 30 ° C. Regarding the course of the reaction, it should be noted that birth of B (OH) ₃ and of OH ions ^" which have the effect of inducing an increase in the pH of the medium during the reduction. However, at high pH values, for example greater than 13, the reduction is slowed down so that it can be advantageous to operate in a buffered medium in order to have a well-fixed reduction speed.

It is by playing mainly on the duration of the treatment that it is possible to easily control the extent of the reduction made. To obtain a resistivity corresponding to the desired values, the duration of the treatment which is necessary is generally quite short and, depending on the proportions of oxide included in the dielectric, it is usually between about a minute and about fifteen minutes. For a given duration of treatment, it is possible to act further on the reduction speed by adding various accelerators to the medium such as, for example, boric acid, oxalic acid, citric acid, l tartaric acid or chlorides of metals such as chloride of cobalt-ll, nickel-ll, manganese-ll, copper-II.

It is also possible to act on the quantity of borohydride used, so as to control the extent of the reduction. A preferred procedure consists in soaking the substrate to be reduced in a more or less viscous borohydride solution, then in removing the substrate to allow the reduction operation to be carried out in air. The quantity of borohydride ions, BH ₄ ^" , consumed depends on the viscosity. BH ^" therefore reacts in a thin layer on the surface to be reduced. This process also has the advantage of not polluting the initial bath, nor of destabilizing it.

The exact and precise conditions for the reduction by the borohydride are as described in EP 82 094. It should however be understood that, in the context of the invention, only a surface part of the dielectric must be reduced.

As a variant, in the case where, by reduction of the particles of copper oxide, a continuous metallic layer of copper is first deposited on the surface of the dielectric, it is possible to carry out an interchange of metals so as to transform the copper layer into a layer of a metal other than copper by oxidation-reduction. This is generally done by bringing the copper-coated layer into contact with an appropriate metal salt, in an acid medium, the condition being that the oxidation potential of the redox couple Cu ₂ 0 / Cu is lower than that of the redox couple of the metal to be deposited.

Another possible embodiment of the sub-layer capable of being metallized can be used. According to this embodiment, the compound capable of inducing a subsequent metallization is an organometallic compound, the sub-layer being obtained by subjecting all or part of the dielectric to the action of a laser or a plasma until obtaining a metal undercoat covering in particular the micro crossings. Before proceeding with the formation of the sublayer, this technique by laser or plasma can also be used to carry out a possible preliminary stripping of the surface of the dielectric so as to make the particles of organometallic appear on the surface.

The metailizations on the sublayers are carried out as described above.

We now detail three preferred embodiments for step B). The embodiments are illustrated by figures representing diagrammatic cross-sectional views of the circuitry produced by a method according to the invention. Figures 1a) to 1g) show the circuitry at the various stages of the method according to the second embodiment.

Figures 2a) to 2h) show the circuitry at the various stages of the method according to the third embodiment. Figures 3a) to 3i) show the circuitry at the various stages of the method according to the first embodiment.

According to a first embodiment, illustrated by FIGS. 3a) to 3i) where a support 301, a circuit level 302 and the dielectric 303 are represented, step B) comprises the steps consisting in:

B1) forming a sub-layer 305 capable of being metallized on the surface of the microtravers 304, and on the surface of the dielectric or part of the dielectric, by subjecting all or part of the dielectric to the reducing action of an appropriate reducing agent up to '' to obtain a metal undercoat covering in particular the microtravers, by reduction of the metal oxide particles on the exposed surface of the dielectric, whose resistivity is between 0.01 and 10 ¹⁰ Ω / D, B2) make a circuitry comprising tracks, pellets, and microtraverses by implementing a sequence of treatment steps comprising, in an appropriate order, the steps (i) of metallization by electrochemical (no current) and / or electrolytic, (ii) selective protection by depositing a protective layer.

Step B1) corresponds to the formation of an underlay according to the second embodiment described above. This sub-layer can, if necessary, be reinforced by an electrochemical and / or electrolytic metallization, in order to obtain a metallic layer 306 on the whole of the dielectric and of the micro-crossings.

Step B2) corresponds to the formation of tracks, pellets and micro-crossings with the implementation of selective protection by depositing a protective layer. This step generally involves a sequence of operations (i) metallization, and (ii) selective protection by depositing a protective layer on a part of the exposed surface of the dielectric. It also advantageously comprises a step (iii) of etching the metal layers or underlay capable of being metallized.

The order of implementation of these operations in the sequence depends on the method used.

Conventionally, one proceeds either by selective metallization of the circuitry (method called "pattern"), or by metallization of the total surface (method called "panel"). The protection method which can be used is not critical according to the invention. It is possible, for example, to use a method consisting in (i) depositing a layer of photosensitive resin on the entire surface of the dielectric or of the sublayer, (ii) forming an image on the photosensitive layer by exposure; then (iii) eliminating the soluble part of said photosensitive resin layer.

Two techniques known from the state of the art are perfectly suitable. The first consists in depositing positive photosensitive resin (positive photoresist) or negative photosensitive resin (negative photoresist) over the entire surface of the undercoat, possibly reinforced with a metallic layer, resulting from step B1 ), then subsequent exposure of the deposited resin layer, in a manner known per se, and according to a predetermined mask, and finally, elimination of the solubilizable part of photosensitive resin, which, as the case may be, consists of the photosensitive resin exposed through the mask (positive photoresist) or made of non-insolated photosensitive resin (negative photoresist). The second technique is the LDI technique called direct photosensitive resin exposure (Laser Direct Imaging).

This technique is advantageous economically since it does not require the use of a mask.

According to this second technique, the photosensitive resin is selectively exposed, pixel by pixel, by a laser beam scanning the surface of the dielectric coated with photosensitive resin.

The soluble parts of the resin are then removed in the same way as for the conventional technique using positive and negative photoresists. Solubilization is often also called revelation. For the implementation of this second technique, two types of laser are for example suitable: a laser operating in the infrared (thermal LDI), a UV laser operating in the wavelength range 330-370 nm (LDI- UV).

Step B2) may more precisely comprise the steps consisting in: B2a) coating with a protective layer certain parts of the surface of the dielectric resulting from step B1), the uncoated parts 309, 308, corresponding to the zones intended for build the desired interconnection circuitry;

B2b) reinforce said parts not covered in B2a) by a metallic deposit 310 complementary by electrochemical means (without current) and / or by electrolytic way; B2c) exposing the upper surface of the dielectric by removing the protective layer deposited in step B2a); B2d) carry out a differential etching of the metal deposited on the dielectric until complete elimination, at the parts of the dielectric which were exposed in step B2c), of the continuous copper sublayer formed at step B1).

Step B2a) will make it possible to selectively strengthen the zones intended to constitute the desired interconnection circuitry on the surface of the dielectric by depositing a layer of thicker conductive metal and generally at least 3 μm. Selectivity is ensured during this stage by protecting future areas without circuitry.

According to a particular process, step B2a) comprises the steps consisting in: B2aα) depositing a layer of photosensitive resin 307 over the entire surface of the dielectric, after treatment with the reducing agent; B2aβ) forming an image on the photosensitive layer by exposure; B2aγ) eliminating the solubilizable part of said photosensitive resin layer. In step B2b) the parts not covered with a protective layer are reinforced by a complementary metallic deposit by electrochemical means (without current) and / or by electrolytic way, this latter way being more particularly preferred.

The metallic reinforcing layer is preferably a copper layer, but the invention is not intended to be limited to this particular embodiment.

However, the deposition of various conductive metals can be envisaged such as the deposition of a layer of nickel, gold, tin or a tin-lead alloy.

Electrochemical metallization (without current) is a known technique which is described in "Encyclopedia of Polymer Science and Technology, 1968, vol. 8, 658-661".

Likewise, electroplating is a conventional technique also described in Encyclopedia of Polymer Science, 661-663.

According to a particularly preferred embodiment of the invention, the metallization, whether electrochemical and / or electrolytic, is continued until a metallic layer having a thickness of at least 5 μm is obtained, preferably a thickness of between 10 and 20 .mu.m. In step B2c), the protective layer deposited in step B2a) is removed in a conventional manner per se. Those skilled in the art will adapt the method of exposure to the type of protective layer used in a manner which is entirely known per se.

Then, in step B2d), a differential etching of the metal deposited on the dielectric is carried out until exposure to the air of the dielectric 314 at the level of the future areas without circuitry which are covered, at this stage of the process. , of a continuous metallic layer with a surface resistivity of 0.01 to 10 ³ Ω / D. then in this step, the areas intended to constitute the interconnection circuitry are engraved in parallel, as well as the future areas devoid of circuitry. However, the thickness of metal covering the zones intended to constitute the interconnection circuitry 312 (track), 311 (conductive microtrack), 313 (patch), being greater than that covering the future zones without circuitry, it is possible selectively "strip" the parts with a small coating thickness.

Etching is generally continued until a final thickness of the metal layer is obtained of at least 3 μm. Advantageously, this thickness is preferably between 5 and 18 μm at the level of the interconnection circuit areas, the remaining areas being perfectly free of metal.

According to a second embodiment, illustrated by FIGS. 1a) to 1g) where a support 101, a circuit level 102 and the dielectric 103 are represented, step B) comprises the following steps: b1) training on the dielectric 103 and on the micro-crossings 104 of a layer of photosensitive resin 105, intended to form the selective protection, this layer not comprising a compound capable of inducing a subsequent metallization d) exposure and revelation of the layer of photosensitive resin so as to selectively discover the microtravers (discovery area 106) and certain parts of the dielectric (discovery area 107) d1) formation of an under layer capable of being metallized 108

- either by contacting with a solution of a noble metal salt capable of being reduced by the metal oxide particles, or by contacting with a reducing agent capable of reducing the metal oxide particles, e1) electrochemical and / or electrolytic metallization in order to deposit a metal layer 109 on the parts discovered during step d) The layer of photosensitive resin can be removed during a subsequent step, leaving a microtross on the surface of the dielectric 113 conductor 110 of lines 111 and pads 112.

According to a third embodiment, illustrated by FIGS. 2a) to 2h) where a support 201, a circuit level 202 and the dielectric 203 are represented, step B) comprises the following steps: b2) formation of a sub layer capable of being metallized 205 on the surface of the dielectric and of the microcrushings 204: either by contacting with a solution of a noble metal salt capable of being reduced by the metal oxide particles, - or by contacting with a reducing agent capable of reducing the metal oxide particles, c2) electrochemical and / or electrolytic metallization in order to deposit a metallic layer 206 on the dielectric and on the microdevices d2) formation on the metallized surface of a layer of photosensitive resin 207, intended to form the selective protection, e2) exposure and revelation of the photoresist layer selectively to uncover parts of the metal layer. A protective layer of resin 210, 209 remains on certain parts of the metal layer. f2) elimination of the metal layer at the parts discovered 208 during step e2) g2) elimination of the photosensitive resin layer. The surface obtained has surfaces of the dielectric 214, conductive micro-crossings 211 through the dielectric, lines 211 and pads 213.

According to another of its aspects, the invention relates to the use of the method according to the invention for producing printed circuits and multilayer modules (commonly known as MCM or muiti chips modules in the art) with high integration density.

Other details or advantages of the invention will appear more clearly in the light of the example given below, only for information, describing the manufacture of a printed circuit.

PREPARATION 1:

In this preparation, the manufacture of a sheet made of nonwoven aramid fibers impregnated with dielectric resin is illustrated. A polyimide-amide resin is produced from trimellic anhydride, diisocyanatotoluene (mixture of isomers 2,4 and 2,6 in the 80/20 ratio) and terephthalic acid (in the molar ratio of trimellic anhydride / terephthalic acid: 60/40).

The diisocyanato on the one hand and the trimellic anhydride plus terephthalic acid set on the other hand are in stoichiometric quantity. This polyimide-amide resin is obtained in a polar solvent which is 1,3-dimethyl-2-imidazolidinone (DMEU). At the end of polycondensation at a rate of 21% dry extract, its viscosity at 20 ° C is 630 poises. The resin / solvent mixture is called collodion.

A nonwoven, consisting on the one hand of KERMEL® polyimide-amide fibers which are not over-stretched and on the other hand of pulp of TWARON® aramid fibers in the 50/50 weight ratio is produced by continuous dry process, at a grammage of 55 g / m ² . This highly calendered hot sheet is then impregnated with the polyimide-amide resin prepared above, using “size press” equipment.

At the outlet of the "size press", the impregnated sheet plunges into a coagulation bath consisting of a DMEU / water mixture in the weight ratio of 60/40 maintained at 20 ° C. The tablecloth thus impregnated is calendered and then washed against the current by a succession of nozzles supplied at the downstream end of the washing system with pure water which gradually takes charge of DMEU as it moves upstream. Part of the washing liquid is used to automatically rebalance the composition of the coagulation bath. After washing, the impregnated sheet is dried continuously in a ventilated oven up to a temperature of 140 ° C.

This sheet, after drying, has an overall grammage of 93 g / m ² . The irregular borders are cut to give a 92 cm wide tablecloth.

PREPARATION 2:

In this preparation, the manufacture of a dielectric loaded with Cu ₂ O is illustrated, comprising an internal layer consisting of a sheet of non-woven aramid fibers, the pickling on the surface of this dielectric, the reduction of Cu ₂ 0 into copper. metallic and copper plating of the resulting dielectric, on both sides. Part of the collodion prepared in preparation 1 is taken and mixed with powdery cuprous oxide.

The weight ratio Cu ₂ O / polyimide-amide collodion is 14.6%. This mixture is passed through so-called "three-cylinder" equipment commonly used to prepare paints. The scraping blade of the last cylinder delivers a suspension of Cu ₂ 0 in the resin, perfectly homogeneous which is used to coat the web impregnated in preparation 1.

The coating is carried out in "full bath" and the carrying of charged resin regulated by a set of 2 rotary cylinders equipped with scrapers.

The composition of the coating resin is kept constant by a pump ensuring its circulation in a loop. In its upward movement, the coated sheet passes through an electric drying oven before coming into contact with the cooled detour cylinder which returns it to the winding station.

The thickness measurement of the coated sheet, determined using a palm, shows a deposit of charged resin of 63 μm on each of the faces of the sheet (assuming that the 2 faces are identically coated).

The sheet thus prepared is passed between 2 abrasive cyclinders rotating in the opposite direction of its movement. The coated tablecloth, with a shiny surface at the entrance, matified in spring with a brighter red color than originally. The tablecloth thus etched on the surface is then reduced by a solution of potassium borohydride. The aqueous reduction bath contains in solution: 0.5% sodium hydroxide, 1% carboxymethylcellulose, 5% potassium borohydride, 1% of an aqueous solution, itself 1% surfactant. The bath is continuously agitated by air bubbling. The sheet is quickly immersed in the reduction bath (contact about 5 s) then the reagent entrained by the sheet in the form of a thin film reacts to the air for about 1 min.

The sheet is then rinsed continuously by passage through a dead bath then subjected to a spraying of double-sided water and finally the liquid surface water is eliminated by passing in front of nozzles for blowing compressed air. The surface resistivity between point electrodes is then between 15 and 30 Ω for a distance of 20 cm.

The sheet thus prepared then passes into a commercial chemical copper plating bath in which detour rollers increase the residence time in the bath. After 15 min of contact, the copper deposit is close to 1 μm on each side of the sheet. This deposit can then be increased by passing it through a galvanic bath of copper sulphate.

PREPARATION 3: This preparation illustrates the formation of circuitry on either side of the metallized dielectric obtained in the previous preparation.

Formats cut from the two-sided copper ply, in Example 2, are then able to be produced in the form of a circuit according to the network plating technology, also called "pattern plating" including: • the calendering of a dry "photoresist" film on each side • sun exposure through masks in contact with the substrate • development using a soft basic solution leaving only the negative part of the mask unchanged

• and finally the electrolytic reinforcement of the exposed copper parts.

The electrolytic reinforcement is carried out in an aqueous bath containing 75 g / 1 of copper sulphate (CuSO ₄ , 5H ₂ O) and 2 moles / liter of sulfuric acid as well as a commercial brightening additive. The anodes of the device consist of plates of pure copper enclosed in bags made of fine fabrics made of synthetic wires. The electrolysis current is fixed at 3 A / dm ² . After ten minutes the electrolytic reinforcement is stopped and the treated format is rinsed. The balance of photoresist film is then dissolved by a strongly basic solution, revealing the desired circuit in excess thickness compared to the thin coppery background. The difference in thickness between these two zones is of the order of 9 μm on each of the faces.

Lastly, the double-sided circuit is immersed in an aqueous bath containing 10% ferric chloride with gentle stirring, and after two minutes, rinsed with water. Only the desired circuit then appears, very matified on a copper-free background. A rapid passage through an acid bath, with 1% sulfuric acid, gives shine to the copper circuits which are then rinsed and dried.

EXAMPLE

The dielectric resin loaded with Cu ₂ O, prepared in preparation 2 is taken up, as well as the double-sided circuit produced in preparation 3. The resin is spread on one face of the circuit using a Meyer doctor blade and dried. by passage in a ventilated oven for 15 min at 190 ° C. The same operation is carried out on the other side then the circuit is pickled by passage between abrasive rollers as in preparation 2. The average increase in thickness of the double-sided circuit is 112 μm, or 56 μm per side assuming an identical deposit. The flatness of the circuit is satisfactory.

Drilling is then carried out on each of the faces, using a C0 ₂ laser, according to a predetermined plan. This drilling is carried out directly without special preparation of the sample. By binocular examination, the holes appear to be roughly circular and with a diameter at the top, of the order of 80 μm.

A reduction and chemical copper plating operation is then carried out as indicated in preparation 2. Finally, the operations described in Preparation 3 are carried out to achieve their end in a multilayer circuit of 4 levels whose layers 1 and 2 on the one hand and 3 and 4 on the other hand are interconnected.

We can then repeat the procedure exemplified above (object of this example) in order to add two new levels of circuits.

Claims

1. A method of producing circuitry comprising conductive tracks, pellets and microtraverses, on the upper surface of a dielectric consisting of a polymer matrix, of a compound capable of inducing subsequent metallization and, where appropriate of one or more other non-conductive and inert charges, said dielectric covering a level of circuitry or a metallized layer, by implementing the steps consisting in:

A) pierce right through said dielectric without piercing the underlying metallized layer or the level of underlying circuitry, so as to form one or more micro-crossings at the desired locations;

B) forming, by metallization, metal tracks, pellets, and micro-crossings on the surface of the dielectric and micro-crossings, with the implementation of selective protection by depositing a protective layer.

2. Method according to claim 1 characterized in that the compound capable of inducing a subsequent metallization consists of metal oxide particles chosen from the oxides of Cu, Co, Cr, Cd, Ni, Pb, Sb and their mixtures.

3. Method according to claim 1 characterized in that the laser drilling is carried out, in step A), using a laser.

4. Method according to claim 1 characterized in that the metallization is carried out on a sub-layer capable of being metallized, previously formed on the surface of the microtraverses, and on the surface of the dielectric or of parts of the surface of the dielectric.

5. Method according to claim 1 characterized in that the compound capable of inducing a subsequent metallization consists of metal oxide particles chosen from the oxides of Cu, Co, Cr, Cd, Ni, Pb, Sb and their mixtures, and in that step B) comprises the steps consisting of B1) forming a sub-layer capable of being metallized on the surface of the microtravers, and on the surface of the dielectric or part of the surface of the dielectric, by subjecting all or part of the dielectric with the reducing action of an appropriate reducing agent until a metallic undercoat covering in particular the microstreams is obtained, by reduction of the metal oxide particles on the exposed surface of the dielectric, the resistivity of which is between 0.01 and 10 ¹⁰ Ω / D,

B2) make a circuit comprising tracks, pellets, and microtravers by implementing a sequence of treatment steps comprising, in an appropriate order, the steps (i) of metallization by electrochemical (no current) and / or electrolytic means , (ii) selective protection by depositing a protective layer.

6. Method according to claim 5 characterized in that step B2) comprises a step (iii) of etching.

7. Method according to claim 5, characterized in that

• during step B1) the sub-layer is formed over the entire surface of the dielectric and of the micro-crossings, this under-layer being if necessary reinforced by a metallization on the whole of the dielectric and of the micro-crossings

• step B2) involves implementing, in order, the following steps B2a) to B2d):

B2a) coating with a protective layer certain parts of the surface of the dielectric resulting from step B1), the parts not covered corresponding to the zones intended to constitute the desired interconnection circuitry;

B2b) reinforce said parts not covered in B2a) by a complementary metallic deposit by electrochemical means (without current) and / or by electrolytic way;

B2c) exposing the upper surface of the dielectric by removing the protective layer deposited in step B2a);

B2d) carry out a differential etching of the metal deposited on the dielectric until complete elimination, at the parts of the dielectric which were exposed in step B2c), of the under-layer formed in step B1) .

8. Method according to claim 7, characterized in that step B2a) comprises the steps consisting in:

B2aα) depositing a layer of photosensitive resin over the entire surface of the dielectric, after treatment with the reducing agent;

B2aβ) forming an image on the photosensitive layer by exposure; B2aγ) eliminating the solubilizable part of said photosensitive resin layer.

9. Method according to claim 5, characterized in that the reducing agent for the formation of the sublayer in step B1) is an alkaline borohydride, the reduction being carried out by bringing said dielectric into contact with an aqueous solution of said borohydride until a continuous layer of metal with a surface resistivity between 0.01 and 10 ¹⁰ Ω / D is obtained.

10. Method according to claim 5, characterized in that the dielectric consists of:

- 10 to 90%, preferably 25 to 90% by weight of metal oxide; - 0 to 50% by weight of inert and non-conductive filler (s); and

- 10 to 90%, preferably 10 to 75% by weight of polymer resin; and in that in step B1) the reduction is continued until a surface resistivity of between 0.01 and 10 ³ Ω / D is obtained, the metallization in step B2) being carried out electrolytically.

1 1. Method according to claim 5, characterized in that the metal oxide particles are cuprous oxide particles, and in that there is deposited, in step B1), a metallic copper sublayer on the exposed surface of said dielectric.

12. Method according to claim 5, characterized in that the metallization in step B2) consists of a metallic deposit of copper.

13. Method according to claim 1 characterized in that the compound capable of inducing a subsequent metallization consists of metal oxide particles chosen from the oxides of Cu, Co, Cr, Cd, Ni, Pb, Sb and their mixtures, and in that step B) comprises the steps consisting of B1) forming a sub-layer capable of being metallized on the surface of the microtravers, and on the surface of the dielectric or part of the surface of the dielectric, by subjecting all or part of the dielectric with the action of a solution of a noble metal salt capable of being reduced by the oxide particles,

B2) make a circuit comprising tracks, pellets, and microtravers by implementing a sequence of treatment steps comprising, in an appropriate order, the steps (i) of metallization by electrochemical (no current) and / or electrolytic means , (ii) selective protection by depositing a protective layer.

14. Method according to claim 2 characterized in that step B) comprises the following steps: b1) formation on the dielectric and on the microstreams of a layer of photosensitive resin, intended to form the selective protection, this layer not comprising no compound capable of inducing a subsequent metallization d) exposure and revelation of the photosensitive resin layer so as to selectively uncover the micro-crossings and certain parts of the dielectric d1) formation of a sub-layer capable of being metallized either by placing contact with a solution of a noble metal salt capable of being reduced by the metal oxide particles,

- Either by contacting with a reducing agent capable of reducing the metal oxide particles, e1) electrochemical and / or electrolytic metallization in order to deposit a metal layer on the parts discovered during step d)

15. Method according to claim 2 characterized in that step B) comprises the following steps: b2) formation of a sub-layer capable of being metallized on the surface of the dielectric and of microtraverses: - either by contacting with a solution of a noble metal salt capable of being reduced by the metal oxide particles, either by contacting with a reducing agent capable of reducing the metal oxide particles, c2) electrochemical and / or electrolytic metallization so depositing a metallic layer on the dielectric and on the microdrives d2) formation on the metallized surface of a layer of photosensitive resin, intended to form the selective protection, e2) exposure and revelation of the layer of photosensitive resin so as to selectively discover certain parts of the metal layer f2) elimination of the metal layer at the parts discovered during step e2) g2) elimination of the photosensitive resin layer

16. The method of claim 1 characterized in that the dielectric surface is obtained from a laminated article comprising a metal layer and a layer of said dielectric, consisting of a polymer matrix, a compound likely to induce subsequent metallization and, where appropriate, one or more other non-conductive and inert charges.

17. Use of the method according to any one of claims 1 to 16 for the production of printed circuits and multilayer modules with high integration density.

18. Circuitry comprising tracks, pellets and microtraverses obtainable by implementing a method according to any one of claims 1 to 16.

19. A printed circuit comprising at least one circuit according to claim 18.

20. Multilayer module comprising at least one circuit according to claim 18.