EP1274880A2

EP1274880A2 - Method for the selective, metal-based activation of substrate surfaces for the wet-chemical metal deposition without external current and a means therefore

Info

Publication number: EP1274880A2
Application number: EP01929548A
Authority: EP
Inventors: Stephan Lange; Veniamin Galius; Stephan Fiedler; Monika Hannemann; Wolfgang Scheell; Herbert Reichl
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2000-04-11
Filing date: 2001-04-11
Publication date: 2003-01-15
Also published as: WO2001077409A2; WO2001077409A3

Abstract

The invention relates to a method for the selective metal-based activation of substrate surfaces for the wet-chemical metal deposition without external current. The inventive method is characterised in that the substrate surface is activated by means of an activator metal which, as such or in the form of a precursor, has been selectively transported to the location of the surface by means of vesicles, whereby said location has to be activated. The invention also relates to a vesicle mixture comprising vesicles that are filled with an activator metal precursor and to vesicles that are filled with a reaction partner for the activator metal precursor. The reaction partner can convert the activator metal precursor into activator metal as soon as the vesicle membranes are opened. Said vesicle mixture is present as such or suspended in a suspension agent and is suitable for use in said method.

Description

Process for the selective, metal-based activation of substrate surfaces for wet chemical, electroless metal deposition and means therefor

The present invention relates to a wet chemical, external currentless method for the continuous or discontinuous generation of thin metallic layers (in particular finely structured layers in the μm-nm range) on organic and inorganic, preferably inert, dielectric substrate support materials such as polymers, ceramics and semiconductor materials, and in particular a method for selective, metal-based activation of these materials as preparation for the subsequent metallization.

Substrates of the type available with thin metallic structures and layers are widely used in microelectronics. They are suitable as function carriers of essential components of rewiring, 5 printed circuit boards or integrated circuits. However, the metallized substrates of the present invention can also be used in optics and microtechnology in general, as well as for decorative purposes or as printed matter.

Metallic structures suitable for the applications described are often produced using a technological sequence of steps based on photolithographic processes. Electromagnetic radiation of a certain wavelength and energy density is projected through a partially transparent structure that acts as a positive or negative template onto the substrate coated with sensitive components (photoresist) over the entire surface. In subsequent etching and rinsing steps, the 5 projected structure is exposed (developed).

Electroplating metal depositions avoiding chemically reactive steps are also known, for example deposition of Pd / Sn colloids from an acidic, colloidal Pd-Sn colloid system on pre-etched plastic, conversion by ion exchange into Pd / Cu and deposition of the desired (noble ) Metal from a suitable electrolyte solution (Paatsch W., metallizing plastics metal surface 1998 5230-34). In so-called additive and semi-additive techniques for the metallization of conductive or non-conductive substrates, in particular the surfaces of organic polymers, ceramics or semiconductor materials, chemical (electroless) metallization processes are also used, which are generally referred to as chemical or chemically reductive processes. For this purpose, the usually inert surfaces of the substrates to be metallized have to be activated if it is a matter of non-active materials such as polymers or ceramics. The activation consists in the application of catalytically active substances or the formation of such substances on wetted layers of the surface in contact with corresponding solutions and suspensions (see, for example, Fundamentals of Microfabrication,

Marc Madou, CRC PressLLC, N.Y., 1997, p. 117). These substances are also called activators. In order to ensure the adhesive strength of the substances acting as activators and that of the subsequent metal layers, the substrate surfaces can be chemically or physically roughened beforehand and thus their surface energy (wettability) can also be changed. Then the surfaces are brought into contact with a solution of suitable metal ions, which are then reduced and deposited as metal nuclei (atomic clusters) and bring about the activation. For this, e.g. Tin and very often used palladium. Finally, metal layers, for example nickel layers, are built up thereon, which are additionally provided with surface protection, e.g. Gold, can be provided. See e.g. Fundamentals of Microfabrication, op. Cit., B. Endres, Galvanotechnik D-88348 Saulgau, 88/1997) No. 5 or ZEV-PCB 7-8 / 97, The new surfaces of the PCB (anonymus).

The activator solution is usually applied to the substrate to be activated by dipping into a solution or suspension containing the activator or one of its precursors. Subsequent dipping steps with further solutions ultimately lead to the generation of the metal nuclei (metal clusters) mentioned on the areas provided for the metallization. Surface activation by incubation directly in precious metal colloids and their destabilization on the surface of the treated substrate is also possible. However, these must be stabilized, because otherwise the individual metal atoms or clusters would aggregate and precipitate out in lumps, grains or layers. (Stabilization of metal colloids or clusters generated in situ is also from other fields of technology such as Synthetic chemistry or exhaust gas treatment known). DE 197 40 431 C1, for example, describes a method using a noble metal colloid which is deposited from a mixture of a corresponding noble metal compound, a reducing agent and a protective colloid. US Pat. No. 3,958,048 discloses an activator suspension which contains a metal compound of a base metal, a hydride as a reducing agent for the metal and an organic dispersing agent, specific pH values having to be observed when reducing the metal compound to catalytically active particles. Colloidal Pd or Pt solutions are described in US 5,332,646; they are obtained by reducing organometallic salts (actually: complex salts) in the presence of

Dispersant produced, which gives the particles a charge and thereby stabilizes them. Between the individual dipping steps, excess components must be removed by intermediate dives (washing steps). This is the only way to prevent the spread of metal germs in the immersion solutions, to avoid coagulation of the colloid and to keep the baths' service life long enough.

DE 197 47 377 A1 proposes a method for preparing the production of very finely structured metallic layers. According to this method, it is provided that metal ions are spatially separated from a further compartment on a substrate, the layer causing the spatial separation containing proteins which can induce a vector-induced light-induced gradient, for example a concentration gradient, which reduce or reduce the metal ions can make a reduction accessible. The gradient is built up and the metal is reduced by selective exposure at those locations where the activation is to take place. If the compartment consists of metal ions packed in vesicles and the vesicle environment, the vesicles must be opened so that the metal can act on the surface of the substrate. This method requires a selective exposure of a part of the layer applied to the substrate in order to enable the required structuring. Classic printing processes can also be used to apply metals directly to surfaces. In this way, stencil printing technology can be used to apply solder deposits (solder bumps, wafer bumping) and form them by remelting. Grid dimensions achieved here are in the range of 200-250 μm (Kloeser, J. et al., Pan Pacific Microelectronics Symposium and Tabletop Exhibition, Mauna Lani (USA), Feb. 10-13, 1998). In the aforementioned development of (screen) printable solders, microparticles are introduced into a polymer matrix and thus achieve the consistency required for printing. When the microparticles fuse, such a matrix can serve as a flow aid. The ones usually used here

However, metal particles (5-75 μm size scale) are not suitable as activators for (wet) chemical metal deposition.

The development of new printing techniques can be found primarily in the area of (color) imaging processes such as light-setting techniques and high-temperature inkjet printing. While the methods determined by exposure depend on the grain size of the sensitive layer and the wavelength of the light used (laser, if applicable), the latter (electroprinting) technology is based on the resolution of 600 dpi that can be achieved with commercially available inkjet printers (which is 25 points / mm corresponds to minimally realizable point distances of 40 μm each). From US 5,853,465 an ink set is known which comprises a microemulsion-based, black ink with water-insoluble pigment and an aqueous, colored ink, the ionic strength of which is higher and which causes the pigment to precipitate on contact with the black ink, thereby causing a Bleeding is prevented. With the creation of colored images from metastable films, which selectively e.g. EP 395096 B1 deals with exposure to a laser beam.

Printing and other dispensing methods have the advantage over a flat treatment of surfaces that a subsequent step for the selective activation of a part of the flat materials can be omitted.

The object of the present invention is to provide a method for the selective, metal-based activation of substrate surfaces, with which, after wet chemical, electroless metallization, very fine-structured metallic layers can later be obtained on a substrate. The method should be carried out using conventional printing or dispensing techniques and at room temperature and should be independent of the material of the substrate to be metallized. In addition, the use of environmentally harmful components should be avoided or minimized where possible, also by reducing the number of process steps and Process chemicals. The realizable structure width should preferably be less than the raster width of about 3 μm that can be achieved in offset printing.

As is known from the literature and already mentioned above, the metal deposition by which the surface to be metallized is activated does not have to be a blanket deposition. It is sufficient to deposit traces of a suitable activator metal on the substrate surface. High precision of the deposition limits should be achievable. The deposited metal nuclei have catalytic activity in the subsequent steps of wet chemical deposition of further materials.

The object of the invention is also to provide a method for metallizing surfaces using this activation method.

The object is achieved by the provision of a method for the selective, metal-based activation of substrate surfaces for wet chemical, electroless metal deposition, characterized in that the substrate surface is activated at the desired locations with activator metal, which as such or in the form of a precursor using vesicles was selectively transported to these places on the surface.

According to one embodiment, the present invention proposes to encapsulate the activator metal as defined below in the interior of liposomes or other vesicles. The activator metal stabilized in this way is applied to the surface to be metallized by a printing process or in another way (dispensing process, stamping techniques). In contrast to surface treatments with later selection of the surfaces to be activated, this material is applied from the outset exclusively to these surfaces. Since the activator metal is encapsulated, the membrane of the vesicles is then opened so that the activator metal reaches the substrate surface. There, it can then be overlaid with metal using conventional, currentless metal deposition processes, for example the additive and semi-additive techniques mentioned in the introduction. Figure 1 illustrates this method using an example. If, according to a second embodiment of the invention, a precursor of the activator metal is used, this is also encapsulated in the interior of the vesicles. They can be converted into the activator metal before or with or after opening the vesicle membrane. At least in the latter case, the vesicles must already have been deposited on the substrate surface at the time of the conversion.

In a third embodiment of the invention it is proposed to use vesicles, the outer side of which is coated with activator metal, which is present in chemical elemental form (as a "metal cluster", see next paragraph), either vesicles that are also in their interior Activator metal or a precursor of

Activator metal, as described for the above embodiments, or preferably contain those vesicles which are free of activator metal or precursors of activator metal in their interior. In this embodiment, the vesicles serve as transport material for the metal nuclei which have already been formed, and if the transport takes place exclusively via the outer surface, the vesicles on the substrate surface need not be opened.

"Activator metal" is to be understood here as meaning metals and metal compounds which have such a chemical and / or physical structure or environment that after application to a surface they have catalytic activity in chemical, electroless metallization baths and thus - catalytically - the deposition of metals can effect from these baths. An important group includes the solid surface modifiers, which are already known in chemically bound form as ions or complex compounds and are known and known as ionogenic activators. Particularly suitable as ionogenic activators are transition metals that can be easily reduced (e.g. from Pd (II) to Pd (0)) and are complexed with redox-sensitive ligands such as nitrite or other oxo, ambident or multidentate ligands. Examples of multidentate ligands are ring-forming diamines or diketonates. Also suitable are e.g. Complexes with metal ions already in the oxidation state "zero", e.g. some

Phosphine. A further, at least partially different activator group comprises the metals, which are present in chemical elemental form and act as atomic clusters on surfaces, which - also - in the first and - exclusively - can be used in the third embodiment of the invention. The expression In the present case, "metal clusters" are intended to mean that a collection of several (preferably at least 10, more preferably at least 25, particularly preferably about 50 to 600) atoms are organized in a composite with a metal character. These can preferably be atoms with a formal valence of zero, but clusters with charge components on the metal can also be used. In addition, reference is also made to LH Gade, coordination chemistry (Verlag Wiley-VCH, Weinheim 1998). On page 528, metal clusters are described as molecules that contain a finite number of metal atoms, which are linked to a significant extent by metal-metal bonds. From the explanations for this it also appears that the metal clusters described there, which are clusters stabilized with ligands, can also be regarded as “metal crystallites” in a ligand shell or as ligand-stabilized colloids at higher metal atom numbers. On p. 543, metal clusters from the series are shown which, due to the packing structure of the metals, have certain preferred metal atom numbers, the so-called "magic numbers". However, it should be clear that the metal clusters suitable for the present invention as activator metal only include those which have the catalytic activity mentioned above in electroless chemical metallization baths. The reference should therefore only refer to the number and structure of the metal atoms.

The metals or metal compounds which can be used in the clusters or ionogenic compounds mentioned are selected with regard to the material to be deposited; they are known to the person skilled in the art. Examples are tin, noble metals or transition metals (e.g. the VIII. Group such as Co, Ni Ru, Rh, Pd, Os, Ir, Pt, the V. group such as Nb and the I. group with Cu, Ag, Au). Suitable ionogenic compounds are, for example, chloro or nitro complexes such as tetranitropalladate with potassium, sodium, lithium or ammonium ions as counterions and palladium chloride.

In the present case, “precursors of the activator metal” are to be understood as meaning those substances which can be converted into activator metal by reaction with a suitable reaction partner at the intended site of action on the substrate surface or beforehand within the vesicles. These are, for example, chelated metals that are dechelated by the reaction partner, complexed metals which are reduced by the reactant (for example those which are described as starting materials for stabilized cluster suspensions in the literature), or metal ions which are reduced by ion exchange, pH change or the like. The reaction partner can accordingly be a reducing agent, for example a reducing agent customary in color or black and white photography, for example 1,4-benzenediamine, 1, 2,3-benzenetriol, m-hydroquinone, p-hydroquinone or p-hydroxyphenylglycine. It is particularly preferred to select a reaction partner which, depending on another chemical property such as the presence of certain ions (in particular the pH value), brings about a reduction in the precursor of the activator metal. This system represents a redox system in which the potentials of the reactants depend on the chemical property mentioned, in particular on the pH value. An example of such a redox system is the combination of palladium (II) amine complex / formate.

In order to convert the precursors of the activator metal into activator metal only at the site of action, several process variants are possible. Thus the reactant, which can convert the precursor into the activator metal, can also be packed in vesicles mixed with the vesicles containing the precursor and applied to the substrate surface. When the vesicles are opened, both the precursor and its reaction partner are released; the conversion to the activator metal takes place. This is in

FIG. 3 shows schematically: vesicles A with a precursor of the activator metal are in a mixture with vesicles B which contain a reaction partner. Separated by the membrane shells of the vesicles, the conversion to the activator metal C is not possible; this takes place only after opening the vesicles on the substrate surface. Alternatively, after application to the substrate surface and opening of the vesicle membrane, the vesicles containing the precursor can be washed with a solution which contains the reactant, which causes the conversion to the activator metal, or the reactant is in the dispersant for the vesicles. This variant is illustrated in FIG. 4, in which vesicle A is shown with a precursor of the activator metal as a dispersion in reaction partner B. Here too, the conversion to the activator metal C takes place only after opening the vesicle membrane on the substrate surface. In order to convert the precursors of the activator metal in the still closed vesicles into activator metal, the vesicles can be brought into contact with a reaction-triggering factor, for example with electromagnetic radiation (for example UV radiation). Alternatively, the concentration gradient of a membrane-permeable ion species, for example of protons, can be used for this purpose, these ions being enriched or depleted in the vesicles, as a result of which the conversion takes place.

The deposition of metal atoms with cluster formation on the vesicle surface for the production of the vesicles according to the third embodiment of the invention can be carried out from preferably aqueous solutions of corresponding metals by reduction according to known methods. The ionic strength of the preferably aqueous dispersion medium used also contributes to the variation of the properties of a vesicle preparation with metal clusters adhering to the outside of the membrane (e.g. with regard to the prevailing charge and therefore presumably also correlates with the binding capacity). The higher the ionic strength, the slower the metal deposition on the surface of the vesicles. If you choose slow deposition, the loading state of the vesicles can be selected very precisely.

The vesicles which are intended for the transport of the activator metal to the site of deposition can be made from any suitable amphiphilic molecules such as lipids or anionic, cationic or in particular nonionic surfactants of natural or synthetic origin in aqueous or non-aqueous liquids be formed. The membrane-forming properties of fatty acids, longer-chain alcohols and lecithin or of phospholipids are known. Preferred is the use of conventional lipid vesicles (liposomes) made of, for example, phospholipid bilayers; however, the choice of suitable substances is not critical and is therefore not restricted to this. Many phospholipids occur in nature in smaller or larger amounts. For example, phosphatidylcholines are found in egg yolk. Most phospholipids fall into two main groups, one comprising a derivatized glycerol molecule and the other having a sphingosine backbone. Natural, but also synthetic phospholipids can be used for the present invention. In addition to phosphatidylcholines, there are, for example, phosphatidylethanolamine, phosphatidylserine or phosphatidylglycerol, but also the synthetic surfactant Cetylpyridinium chloride suitable. For reasons of cost, egg lecithin or plant-derived phospholipids such as soybean lecithin, but also cholesterol or glycolipids are suitable. In addition to lipids or lipid mixtures, the liposomes can also contain further constituents. For example, substances such as cholesterol or other substances which have hydrophobic or hydrophobic regions and which, for example, influence the permeability and flowability of the membrane can be embedded in a lipid membrane. When the term "liposomes" is used in the present application, this is not meant to be limited to lipid vesicles; rather, all vesicles, including those made of other materials, for example the “niosomes” ¹ formed from nonionic surfactants, are to be included. Tetraalkylammonium compounds may be mentioned as an example of synthetic amphiphiles; Representatives of these compounds are the dialkyldimethylammonium halides (chlorides, bromides), from which vesicles suitable for the invention can be produced.

In order to vary the properties of vesicle preparations of the present invention, the membrane-forming substances can also contain charged or uncharged head groups-carrying synthetic compounds and substances of natural origin with one or more long-chain (C ₆ -C ₂₀ preferably C ₁₂ -C ₁₈ ) saturated or also simply or include polyunsaturated side chains. The head group can be, for example, an amine coupled via a phosphoric acid ester bond (choline, ethanolamine, etc.).

The crystallinity (liquid crystal - gel phase transition) and the charge of the membrane are the decisive variables which are responsible for the adsorption of metal clusters at least on the outer surface of the vesicle and also for their further growth. The nucleation (the locally occurring growth process) of metal clusters on surfaces by coalescence of individual atoms takes place here on a liquid-crystalline surface. Among other things, the typical characteristics of the membrane former (used as a liposome base) influence the characteristics of the clusters growing on the vesicle surface. An essential one

¹ The term "niosomes" is derived from a combination of the terms "nonionic" and "(lipo-) somes" A factor for the targeted influencing of the degree of order / mobility of membrane formers as typical as phospholipids is the temperature, but also the presence of factors forming membrane domains (eg proteins or cholesterol).

The liposomes usually have diameters in the range from about 10 nm to about 1 μm, more preferably from about 50 to 500 nm and typically about 100-200 nm. In an essential embodiment, they are with a solution of the ionogenic compound (or a mixture of several such Compounds) or a suspension of metal clusters or a precursor of the activator metal. In a further embodiment, the activator metal adheres to the outwardly facing side of the lipid bilayer of the liposomes. The activator metal can be attached to the outside of the liposomes in addition or as an alternative to filling the vesicles.

A solution of ionogenic activator metal, a metal suspension or an activator metal precursor can be encapsulated by known methods. For example, the lipid intended for the liposomes and the corresponding metal salt of the ionogenic activator, optionally with the addition of further salts / components, such as potassium or sodium salts, to adjust the ionic strength required for the stability of the vesicles or charged surfactants for the purpose of a defined charge of the vesicles , placed in water, and a liposome suspension is produced using a common method. Polymeric stabilizers can also be added. Possible manufacturing processes for the liposome suspension (also known as dispersion or emulsion, since such systems do not fit into the traditional solid / liquid or liquid / liquid system) are, for example, extrusion processes, high-pressure filtration techniques, high-speed filtration techniques, homogenization techniques, ultrasonic processes or high-speed stirring. The non-encapsulated ionogenic activator can, if desired, be removed from the suspension by washing or filtering the suspension or by column chromatography or by a dialysis method. An encapsulated metal cluster suspension with activator metal properties is not known in the prior art. However, it can be generated, for example, in situ in the vesicles, as in the simultaneous with the present application filed by the same applicant, "Activator metals encapsulated in vesicles and process for their preparation" presented and claimed in detail and shown here in an example (see also FIG. 2). Furthermore, it can be produced by direct encapsulation, for example with the aid of a high-speed dispersion process, which is also mentioned in the above

Registration is described in more detail. The encapsulation with the aid of such or a comparable method during or immediately after the formation by reduction can therefore largely or completely dispense with other stabilizers, since the large surface area of the clusters is protected from undesired reactions by the rapid encapsulation.

The metal cluster suspension obtained can be cleaned of constituents of the starting components, as already described above for the encapsulated ionogenic activator. A liquid, possibly also pasty product is obtained, which may already as such, i.e. without further formulation, can be used as a printable paste.

In order to load the outer surface of the vesicles with metal clusters, the vesicles are brought into contact with a solution of a corresponding metal compound, whereupon the metal atoms are brought into a state either by reduction or by release of the metal atoms from metal atom complexes already in the formal oxidation state "0" from which they aggregate into clustem. Examples of suitable metal compounds for this are those which have been described in detail above under "precursors of the activator metal", that is to say all those substances which can also be converted into activator metal by reaction with a suitable reaction partner at the intended site of action on the substrate surface or within the vesicles. These are also suitable for use in solutions in which the outside of the vesicles can be loaded with metal clusters, regardless of whether the vesicles also contain metal in some form or not.

It has been found that the reduction of metal salts from an aqueous solution in which closed vesicles are suspended can be slowed down and thus becomes accessible to fine regulation. It can be assumed that the the underlying mechanism is different from that which effects the stabilization of metal clusters with low molecular weight stabilizers such as citric acid or high molecular weight polymers such as PVP or PVA. The stabilizing effect of the vesicles is probably based on the adsorption capacity of charge carriers for cluster precursors (complex) ions which freely diffuse within the vesicle membrane (laterally) and / or growing atomic clusters.

The quantitative ratios of the liposome reaction batch also determine the characteristics of the metal clusters growing on the vesicle surface. In addition to the concentrations (the ionic strength), the type (e.g. value) and the pH of the aqueous dispersion medium influence the effective surface charge (zeta potential) of dispersed microparticles, including liposomes and other vesicles. These parameters can therefore be used specifically to control the growth of the metal clusters on the vesicle surfaces.

Since on the one hand the suspensions of vesicles and solution of the metal compound as such are generally stable, on the other hand metal clusters from a critical size of about 5 atoms onwards no longer disintegrate, the corresponding reaction can be “switched on” at any time and usually by reversing the chemical conditions can also be "switched off" again. This allows the desired amounts of metal to be deposited and thus also the cluster size or amount to be controlled very well, especially since, as mentioned above, the rate of the reaction can be regulated via the ionic strength of the suspension. This can be clearly seen from the example of a reduction of Pd by formate: the reaction can be controlled via the pH value. Acid addition to the neutral suspension of

Vesicles in the palladium complex solution cause the reduction to start, the addition of bases stops them. The addition of salts slows them down.

If the liposomes have been separated from their suspension by one of the abovementioned steps, they can then be resuspended. The viscosity of the suspension is easily adjustable at room temperature. This can be done, for example, by adjusting the ratio of liposomes to suspending agents. The suspension can thus be concentrated by customary methods in order to bring its viscosity to a value which it can use as a printing paste or for other application makes suitable. Alternatively, a thickener such as polyvinylpyrrolidone can be added to the suspension. The liposome concentration is chosen in a suitable manner by the person skilled in the art and is usually in the range between 0.1 and 50% by weight. It is favorable to bring the liposome suspension obtained to a slightly oily (spreadable) consistency similar to conventional offset inks, which allows existing methods and machines to be adapted to the method according to the invention. In particular, it can be adapted for layer deposition in microelectronics.

The substrates that can be prepared for the metallization using the method according to the invention are not restricted. Examples are polymers such as cyanate esters, phenolic or epoxy resins, polyimides, phenolic resins or benzocyclobutensiloxanes, ceramics or semiconductor materials. Such substances are used in microelectronics. The coating of surfaces made of polymer materials is increasingly gaining economic importance; both organic and inorganic-organic polymers can serve as a substrate. The present method is particularly suitable for the production of wiring structures on printed circuit boards or foils for multilayer printed circuit boards.

The technique with which the liposomes loaded with activator metal are selectively applied to the surface of the substrate to be activated is also not critical. So all common printing techniques, but also stamping techniques or the like can be used. The stamp used can be profiled and homogeneously wettable or consist of an almost planar surface that has selectively wetting areas due to chemical modification (modern offset principles). A technique well suited to the present invention is offset printing. The expected resolution of the structures that can be applied depends on the printing technology and the printing press used as well as the consistency of the liposome paste. Structures with widths and distances down to a few 10 to 100 nm are available. The minimal edge blur is in the range of the liposome diameter. With the method according to the invention, surface unevenness such as depressions and openings (eg bores) that go beyond material roughness can be wetted and filled.

After the liposome paste has been applied, it is dried for fixation, the choice of drying parameters (temperature, time) being suitably based on the properties of the liposomes. The drying step can be designed so that the liposome content is released. This is possible, for example, by incubating the substrate provided with the liposome paste at approximately 60-80 ° C. Such an incubation is commercially available

Metallization baths (e.g. nickel-phosphorus, nickel-boron or copper bath) are a common step. It is therefore advantageous for the first and the second embodiment of the invention if the lipids used for the preparation of the liposomes have a phase transition temperature below the temperature range required for the metallization and the incubation in the metallization bath is preceded by the usual conditioning rinsing baths which bring about an opening of the liposomes. Alternatively, the printed liposome paste can be rinsed with a membrane-lytic medium. Numerous surface-active substances (surfactants) such as Saponins (Menger, F.M. et al., Angew. Chemie 1998, 110, 3621-3624) or organic solvents are known for their membrane-lytic properties and are used in biochemical working techniques. As further measures for the lysis of the vesicles, their exposure to electromagnetic radiation (UV, IR) or treatment in (reducing) low-pressure plasma are suitable. The lytic measures mentioned can also be combined in a suitable manner if necessary.

The membrane lysis need not be complete; it suffices to create perforations or "holes" through which the contents of the liposomes come into contact with the environment.

Before the lysis, the applied liposome paste can, if necessary, be cured, in which case it must contain appropriate constituents, for example thermally or radiation-induced curable mono- or polymers. Before the liposome suspension is applied, the substrate is preferably pretreated. Layers obtained after pretreatment are generally more stable because the adhesion is improved. The pretreatment steps depend on the chemical composition of the substrate. For example, the roughening of the polymer surface by dissolving / swelling - etching - cleaning is effective (Schröer, D. et al., Electrochimica Acta 1995 40, 1487-1494; or Schmidt, R. et al., Galvanotechnik 1996 87, 2015-2022) ,

The surface activation of printing technology described according to the invention is easily divided into known and industrially practiced process sequences, so that its detailed description can be dispensed with here. (See Suchentrunk, R. Metallizing of Plastics- A handbook of Theory and Practice Finishing Publications Ltd 1993; DE 196 39 898 A1). The substrate, which is preconditioned according to common processes, is directly suitable for building up metal layers in corresponding commercial autocatalytic baths (e.g. Schmidt-Nickel 604 from Herbert Schmidt GmbH, Solingen, Federal Republic of Germany). The method according to the invention differs as a purely additive method from conventional stamping techniques on copper-clad material in that the etching steps necessary in these subtractive techniques are completely eliminated here. The elimination of etching-back steps is associated with a saving of (expensive and specially treated) activator material. A major advantage lies in a reduced number of required process steps and reduced costs for process wastewater treatment. Another advantage is the stability of the activator suspension used as the "pressure medium". And finally, with the method according to the invention, there is the possibility of filling superficial unevenness of the printing material (depressions and openings, such as those represented by blind holes and "vias" on printed circuit board material).

The invention will be explained in more detail below using exemplary embodiments. example 1

L-α-phosphatidylcholine type II-S from soybeans, Sigma catalog No. P5638 is at a concentration of about 5% in an aqueous solution of 10 mM K ₂ [Pd (NO ₂ ) ₄ ] and 0.2M K ₂ SO ₄ pre-swollen The mixture is subjected to an ultrasound treatment or homogenization, whereby lipid vesicles are formed, in the interior of which the metal activator is enclosed.

The lipid vesicles are chromatographed using a NAP-25 pre-filled gel cartridge (Amersham Pharmacia Biotech). The solution is freed from potassium nitropalladate.

Thin panes or foils of glass fiber reinforced epoxy resin polymer (so-called FR4) are incubated at room temperature for 5 minutes in a 20% aqueous solution of the adhesion promoter LUPASOL SK (BASF AG) in order to improve the adhesion. The liposome paste prepared as above is applied to the dry substrate using a stamp. A 1-2 minute drying at 80 ° C. then takes place for fixation, the liposome membrane opening. The subsequent deposition of an electrically conductive metal layer is carried out without current in a commercially available autocatalytic metallization bath (e.g. chemical nickel 604, Herbert Schmidt GmbH & Co. Germany).

After the incubation period prescribed for such baths, a uniformly adhering nickel layer is formed at the areas printed with the liposome paste, which, depending on the intended area of application, is available for subsequent treatment (e.g. deposition of a copper or gold layer).

FIG. 5 shows a stamp impression of a liposome paste on printed circuit board base material FR4 produced in accordance with Example 1, which was reinforced in the nickel bath. Example 2

A solution containing 2 mM tetramminopalladium dichloride and 200 mM potassium formate and having a pH of 8 is mixed with lipid in an amount of 0.2 to 40% by weight, based on the total weight of the solution. The mixture is treated with ultrasound, resulting in lipid vesicles filled with solution. After separating the outer solution and replacing it with an osmotically equivalent solution that is free of the redox system (osmotic compensation by means of potassium sulfate or glucose), the chemical equilibrium of the redox system is increased by adding a suitable acid (slow dropwise addition of 0.5 M sulfuric acid until the pH Value has dropped to 5) moved to the palladium reduction side. Finely dispersed palladium particles form within the lipid vesicles.

The liposome suspension thus obtained is stable. Their consistency (viscosity) depends on the amount of lipid used. It ranges from thin, watery (0.2 to 5% by weight lipid) to filthy-viscous (approx. 40% by weight lipid) and can be conditioned directly for stamp application. After the stamp imprint has dried on, the substrate can be used for the selective deposition of metal layers as described above.

Examples 3-5

A liposome dispersion was made from soybean lecithin (II-S "Asolectin" from SIGMA-Aldrich, catalog number P-5638) and aqueous using the conventional methods (ultrasonic generator of the type "Bransson Sonifier 450, output stage 3, duty cycle 30%) Salt solutions of different concentrations: A1: 0 mol / IK ₂ SO ₄ in distilled water A2: 100 mmol / l K ₂ SO ₄ in distilled water A3: 500 mmol / l K ₂ SO ₄ in distilled water. For this purpose, 500 mg of lipid in 20 ml of the aqueous salt solution were pre-swollen with stirring for about 1 hour and then sonicated in a test tube for 10 minutes. Furthermore, stock solutions from

B: 50 mmol / l tetraammine palladium (II) chloride ([Pd (NH ₃ ) ₄ ] CI ₂ ) in dist. water and

C: 5 mol / 1 potassium formate (HCOOK) prepared.

Then 18 ml of the liposomes in solution A1 or A2 or A3 with 3 ml of dist. Water, 6 ml of solution B and 3 ml of solution C are added at room temperature with constant stirring (magnetic stirrer).

The pH of the homogeneous dispersion (according to pH 7.85) was then adjusted to pH 4.8 using (about 3 ml) 0.1 mol / IH ₂ SO ₄ . The mixture was then continuously stirred in a water bath at 35 ° C. (magnetic stirrer). With the onset of metal cluster formation on the outer surface of the lipid, recognizable, for example, from a gradual browning of the mixture, aliquots were removed at intervals of 5 minutes and a pH of 8.0 was adjusted therein by adding 0.1 mol / l aqueous KOH in each case , Depending on the chosen point in time of stopping the reaction by resetting the pH in the reaction mixture to pH> 8.0, metal clusters of different sizes can be obtained in this way. The following picture emerges: The amount of the metal growing in cluster form on the surface of the liposomes increases with the course of the reaction over time. With the same reaction time, the amount decreases with increasing salt concentration of solutions A. The reaction with solution A3 is therefore best suited to bring about a precise adjustment of the amount of metal deposited by specifying the corresponding reaction time.

Claims

Expectations :

1. A method for the selective, metal-based activation of substrate surfaces for wet chemical, electroless metal deposition, characterized in that the substrate surface is activated with activator metal which, as such or in the form of a precursor, was selectively transported to the surface to be activated with the aid of vesicles ,

2. The method according to claim 1, characterized in that the vesicles with paste-like consistency suspended in a suspending agent on the

Substrate surface are applied.

3. The method according to claim 1 or 2, characterized in that the vesicles are loaded with activator metal enclosed inside and the activator metal is deposited on the substrate surface by opening the vesicle membrane.

Method according to one of claims 1 to 3, characterized in that the vesicles are loaded with activator metal adhering to their outer surface.

A method according to claim 1 or 2, characterized in that the vesicles are loaded with a precursor of the activator metal which is enclosed in their interior and the precursor is converted into the activator metal when or after opening the vesicle membrane with the aid of a suitable reaction partner.

A method according to claim 5, characterized in that the reactant was previously enclosed in vesicles which were transported and opened together with the vesicles containing the precursor of the activator metal to the desired location on the surface.

7. The method according to claim 5, characterized in that the conversion of the precursor of the activator metal into activator metal takes place in that the substrate surface is then rinsed with a solution which contains the suitable reactant, or the reactant is dissolved or suspended in a suspending agent for the vesicles is present and after

Opening the vesicle reacts with the precursor of the activator.

8. The method according to any one of claims 5 to 7, characterized in that the precursor of the activator metal from at least one salt, ion pair, oxide or hydroxide or at least one complex compound of a metal, selected from transition metals and noble metals of I., V. and VIII. Subgroup, and preferably consists of a complex compound of Pd (II).

9. The method according to claim 1 or 2, characterized in that the vesicles are loaded with a precursor of the activator enclosed in their interior and either a factor which triggers the conversion into activator metal, preferably UV or other electromagnetic radiation, or a concentration gradient of a membrane-permeable ion species , e.g. of protons, the enrichment or depletion of these ions inside the vesicles causing the conversion into activator metal.

10. The method according to any one of claims 1 to 3, characterized in that the activator metal consists of at least one ionogenic activator or of metal clusters.

11. The method according to claim 10, characterized in that the metal clusters are encapsulated without organic polymers in the vesicles.

12. The method according to any one of claims 2 to 11, characterized in that the vesicles using a printing technique, preferably selected from offset, sieve,

Gravure and flexographic printing are applied to the substrate surface.

13. The method according to any one of claims 2 to 11, characterized in that the vesicles are applied to the substrate surface with the aid of a dispensing technique, preferably selected under inkjet printing and "electroprinting".

14. The method according to any one of the preceding claims, characterized in that the vesicles suspended in a suspending agent are applied to the substrate surface, which contains at least one further organic constituent which chemically, thermally or radiation-induced curing of the suspension obtained on the

Enables substrate surface, and after application of the suspension is cured in a suitable manner.

15. The method according to any one of the preceding claims, characterized in that the vesicles are lipid-containing or consisting of lipids vesicles.

16. The method according to claim 15, characterized in that the vesicles are opened by lysis of the liposome membrane.

17. The method according to any one of the preceding claims, characterized in that the surface of the substrate has previously been treated with at least one rinsing or conditioning liquid which brings about an improvement in the adhesion properties of the substrate surface to the activator metal.

18. The method according to any one of the preceding claims, characterized in that the vesicles are opened in a rinsing or conditioning step, which is a step required for a subsequent metallization, the rinsing and conditioning being carried out with the aid of a liquid at a temperature at which the vesicles are opened.

19. The method according to any one of the preceding claims, characterized in that the substrate is a material acting as a circuit carrier in microelectronic assemblies.

20. A method for the wet chemical electroless deposition of metallic layers on substrate surfaces, comprising the steps:

(a) activating at least a part of the substrate surface using a method as defined in one of claims 1 to 19, and

(b) Metallizing the activated areas of the substrate surface in a wet chemical, electroless plating bath.

21. vesicle mixture comprising vesicles filled with an activator metal precursor and vesicles filled with a reactant for the activator metal precursor, the reactant being able to convert the activator metal precursor into activator metal as soon as the vesicle membranes are opened.

22. vesicle suspension containing a vesicle mixture according to claim 21 in a suitable suspending agent.