WO1993020263A1

WO1993020263A1 - Method of metallizing non-conducting surfaces, in particular circuit boards

Info

Publication number: WO1993020263A1
Application number: PCT/DE1993/000309
Authority: WO
Inventors: Reinhard Deboer; Hans-Joachim Grapentin
Original assignee: Atotech Deutschland Gmbh
Priority date: 1992-03-31
Filing date: 1993-03-27
Publication date: 1993-10-14
Also published as: DE4211152C1

Abstract

The method proposed for metallizing non-conducting surfaces is characterized by the following operations: a) treatment of the surface with a chelating agent and/or an organic ionogenic compound; b) treatment with a solution containing a precious metal plus, optionally, one or more reducing agents; c) treatment with a solution containing manganate and/or permanganate; d) treatment with an acid solution containing monomeric and/or oligomeric pyrrole compounds; e) electrolytic metallization.

Description

Process for metallizing non-conductors _/ especially printed circuit boards

The invention relates to a method for metallizing non-conductors.

Methods for the production of non-conductors, in particular plated-through circuit boards, are known within the prior art. Processes are described in the documents DE-PS 37 41 459 and EP-AI 0398 019 in which catalytically activated surfaces of the base material are produced, in which the catalytically activated surfaces are conditioned before the galvanic metal deposition. This conditioning is carried out with a solution containing one or more polymeric organic ionogenic compounds. The teaching of these documents also includes activation by means of precious metal-containing, colloidal, ionogenic or non-ionic catalysts, in particular the known catalysts based on palladium and / or tin.

Newer processes for the metallization of non-conductors are based on the fact that polypyrrole is a conductive polymer. This polypyrrole can be applied as a first layer to a non-conductor instead of "chemical copper", followed by the galvanic metallization processes, for example galvanic copper plating. Within the documents EP-AI 0 206 133, DE-OS 39 31 003, DE-PS 38 06 884 and PCT / DE 00920 (WO 91/08324) methods for the direct metallization of non-conductor surfaces by the application of a treatment with oxidizing agents, for example potassium permanganate, and a heterocycle solution, for example pyrrole solution. When this process is carried out, a conductive organic polymer, for example polypyrrole, is deposited on the non-conductor surface. This polymeric conductive layer adheres firmly to the surface of the non-conductor and can be galvanized immediately.

According to the teaching of these documents, a conductive polymer layer on non-conductors can only be produced if an adhesive layer of oxidizing agents has been applied beforehand. Usually, the method is used that the non-conductor is treated with an alkaline permanganate solution, in particular when an epoxide is used as the non-conductor, this is oxidized and a manganese dioxide layer is formed on the surface, which in turn serves as an oxidizing agent for the formation of conductive polymers (when contacting) with heterocycles).

Not all materials, such as cyanate esters, higher crosslinked epoxides with a Tg higher than 140 ° C, epoxies with BT additives, Teflon, certain polyimides and polyamides, polystyrenes, polyethylenes, polycarbonates, block merisates made of acrylonitrile butadiene Styrrole (ABS), polyester or polysulfones, or also fillers such as glass, ceramic, aluminum oxide, titanium dioxide or barium sulfate form a layer of manganese dioxide directly and easily with the permanganate solution. There is therefore a need within the prior art to also be able to process these materials without problems.

The object of the invention is to provide a method in which a uniform and homogeneous metallization can be achieved in the shortest time, in particular in the drill sleeves, and which is suitable for processing almost all conventional non-conductor materials. This problem is solved according to the teaching of the claims.

The method according to the invention for metallizing non-conductors is characterized by the following method steps:

a) optionally treating the non-conductor with a cleaner and / or etching cleaner,

b) treatment of the non-conductor with a chelating agent and / or an ionogenic organic compound,

c) treatment with a noble metal-containing solution, in particular palladium-containing solution, optionally contain one or more reducing agents,

d) treatment with a solution containing manganate and / or permanganate,

e) treatment with an acidic heterocycle-containing solution, in particular pyrrole solution,

f) electrolytic metallization.

Furthermore, the invention includes the use of a noble metal-containing solution, in particular a palladium-containing solution, as a process step together with the steps of a manganate and / or permanganate and pyrrole treatment in the metalization of non-conductors, in particular printed circuit boards.

It has been found that the method according to the invention can advantageously be used in horizontal continuous systems which are operated continuously.

Within the process according to the invention, all commercially available products can be used as cleaners and / or etching cleaners. Such solutions which contain persulfate and / or acid, in particular sodium persulfate and mi mineral acid, such as sulfuric acid.

The treatment of the non-conductor with a chelating agent or an ionogenic organic compound generally takes place with nitrogen-containing derivatives. These derivatives can be used with advantage, which are already described as conditioning agents for the treatment of base materials in the documents DE-OS 35 30 617 and DE-OS 41 12 462. These are quaternary organic nitrogen compounds that can contain a vinyl or allyl group. However, the corresponding polymeric compounds can also be used (polymerized via the respective vinyl or allyl groupings). Examples of suitable are the N-methyl-N * -vinyl-imidazolinium metosulfate, N-methyl-N'-vinyl-pyrrolidonium chloride, N-allylimidazolium iodide, N-methyl-N'-vinyl-Σ-caprolactam quarter salt, N-butyl-N'-allylbenzimidazolinium methosulfate, the copolymer of N-methyl-N'-vinylimidazolinium methochloride and vinylpyrrolidone, and the homopolymers of the listed types of compounds or other salts.

Suitable chelating agents are, for example, ethanolamine, triethanolamine, amino acids (e.g. glycine) or hard complexing agents, such as EDTA.

The treatment with a noble metal-containing solution, in particular a palladium-containing solution, optionally containing one or more reducing agents, is carried out after the treatment with an ionogenic organic compound. All commercially available products can likewise be used as noble metal-containing solutions, it being irrelevant whether the respective noble metal is in colloidal form, is stabilized with tin or organic polymer or is ionic, for example described in EP-A-0317 092, PCT / DE 90/00845 and DE-Al 16 18 299. These activations by means of catalysts containing noble metals can be carried out in one or more stages. A solution consisting of:

20-2000 mg / 1 palladium, preferably 100 mg / 1, stabilized with a polyvinylpyrrolidone with a molecular weight range of 1000-10,000,000, preferably 10,000. The ratio of metal to polymer can be between 3: 1 and 1: 100, preferably 1:10. The production of such colloids containing noble metals is described in the documents EP-A1-0 187 962 and EP-A1-0 163 831 .

The use of these solutions containing precious metals is advantageously possible in water for economic and ecological reasons. However, solvents or solvent mixtures that can be mixed with one another and with water are also used. The advantageous pH of these activation solutions is between pH 1-3, preferably between 1.5-2.0. The work is usually carried out at a temperature between 30-80 ° C, preferably 30-50 ° C.

The noble metal-containing solution may be sensitive to oxidation, so it can be used to redissolve the palladium, e.g. B. come as palladium chloride. The introduction of oxidizing agents is prevented by treating the non-conductor with a dilute solution of a reducing agent before the treatment with the metal colloid. In addition, it can be advantageous to regularly add small amounts of reducing agent to the metal colloid or to select generally reducing conditions. Particularly noteworthy is the embodiment in which the reduction potential in the metal colloid solution is permanently monitored by means of an electrode and is kept at a constant value by the reducing agent by means of automatic replenishment. This procedure has proven to be particularly advantageous for the reducing agents (such as, for example, hydrogen boron compounds and hypophosphite), which can be catalytically decomposed by the noble metal colloid. In this case, the hydrogen formed during the decomposition takes over the oxide tion buffering against the oxidizing agent.

As a further process step, treatment with a manganate and / or an ananate solution follows. As a rule, a solution is used which contains manganate in the concentration 10-75 g / 1, permanganate in a concentration 30-150 g / 1, and sodium hydroxide in a concentration of 40-70 g / 1. However, it is also possible to use solutions which contain only manganate or only permanganate. The treatment with manganate / permanganate solution can also take place in an acidic medium, in particular a weakly acidic medium.

The next step in the process is treatment with a weakly acidic pyrrole solution. The pH of such a solution is usually between pH 1.5 - 4.00.

As an alternative to the one-stage treatment with an acidic pyrolytic solution, this step can also be carried out in two stages. Either treatment is carried out first with a pyrrole solution and then with an acid solution (described in DE-PS 38 06 884) or first with an acid solution and then with a pyrrole solution. However, the one-step method has given the best results.

The subsequent galvanic metal deposition is carried out using known galvanic baths. In principle, all metals or alloys that can be deposited by electroplating can be deposited. However, copper electrolytes are preferably used. Sulfuric acid copper baths with a content of 50-300 g / 1 sulfuric acid and a metal content of 5-50 g / 1 are particularly preferred. But also fluoroboric acid, hydrochloric acid thiosulfate- or pyrophosphate-containing or cyanide electrolytes, as well as electrolytes based on sulfonamides and organic sulfonic acids have proven to be well suited.

Electrolytes are operated under the usual conditions, namely in the temperature range between 20 and 70 ° C., with current densities between 0.1 and 20 A / dm ² . Surprisingly, the time of the galvanic deposition can be shortened considerably, namely in particularly favorable cases to <2 min. This gives uniform, closed and, moreover, firmly adhering metal layers which have no defects either in the so-called transmitted light test.

The plated-through circuits produced according to the invention can be processed in a known manner. For example, a further build-up of metallic layers can be carried out galvanically, so that copper layers of 25-40 μm are formed, which are then covered with further metallic layers which are applied to the printed circuit boards as etching resists .

The following examples are intended to illustrate the invention:

Example 1

A drilled, copper-clad printed circuit board, the non-conductor (the base material) consisting of normally cross-linked epoxy with glass as the filler, is subjected to a back-etching process ("smear removal"), as is customary in multilayer circuits. The etch-back is independent of whether it is a plasma, permanganate-sulfuric acid, chromic acid process or a corresponding combination process.

The bores of the circuit board pretreated in this way, in which epoxy was etched back and the filler glass was exposed, are metallized using the following methods.

Time temperature

1. Etching cleaning (e.g. based on 0.5 min 30 sodium persulfate / sulfuric acid)

do the washing up

2.Clean (without conditioning) 0.5 min 70 ° C pH about 12 (0.5 - 5 min

do the washing up

3. Oxidation formation with the aid of 2.5 minutes at 85 ° C. of an alkaline permanganate solution (0.5-5 minutes)

(60 g / 1 KMn0 ₄ and 25 g / 1 K ₂ Mn0 ₄ ) rinse

4. formation of a conductive layer by means of a monomer / oligomer (0.5 to 5 min) stabilized pyrrole solution (pH 2) at 0.5 ° C. Rinsing 5. Copper cleaning 0.5 min 25 ° C

(5 vol.% Sulfuric acid) (0.5 - 3 min)

Electrolytic metallization *, 27 z. B. with an acidic copper electrolyte

Rinse / dry

* In the examples, the current density was kept constant at 2 A / dm ² for simplification. A conventional cleaner suitable for epoxy but not containing any of the compounds described with conditioning properties was used as the cleaner.

After 30 minutes of electrolytic copper plating, which corresponds to a copper deposition of about 10 μm, no 100% coverage, especially of the glass fiber, could be determined. This result could not be improved even if the pH of the cleaner was varied from alkaline to neutral to acidic.

Example 2

Example 1 was repeated, 2 g / 1 Basotronic PVI ^R (product from BASF AG) being added to the cleaner.

The occupancy of the epoxy was almost 100%, that of the glass fiber better, but not yet closed. Example 3

Like example 2, but with an additional so-called pre-activation according to the following workflow:

1. Etch cleaning 0.5 min 30 ° C

200 g / 1 sodium persulfate

+ 15 ml / 1 sulfuric acid, 96% by weight

do the washing up

2.Cleaning / conditioning (pH 11-12) 5 g / 1 sodium carbonate 0.5 min 70 ° C + 2 g / 1 Basotronic PVI ^R (poly-N-methyl-N - (vinyl) _n - imidazolinium compound) rinse

Preactivation (pH 2) 1.0 min 40 ° C 100 mg / 1 palladium as chloride + 1 g / 1 polyvinylpyrrolidone + 5 g / 1 sodium hypophosphite

do the washing up

4. Potassium permanganate solution 0.5 min 87 ° C 50 g / 1 KMn0 ₄ 25 g / 1 K ₂ Mn0 ₄ 55 g / 1 NaOH

do the washing up

Conducting layer formation for 0.5 min using a stabilized monomeric / oligomeric pyrrole solution (PH 2)

do the washing up 6. Sulfuric acid decapping (5 vol.%) 0.5 min 25 ° c

7. Electrolytic metallization 30 ° C z. B. with an acidic copper bath

Rinse / dry

Already after three minutes of electrolytic copper plating, 100% coverage was achieved.

Example 4

Example 3 was repeated using an acidic potassium permanganate solution (pH 4) which was stabilized with phosphoric acid.

After approximately five minutes of electrolytic copper plating, the boreholes were 100% occupied.

Example 5

As example 3 using the following non-conductors:

Epoxy with Tg> 130 ° C, special epoxy (CEM 3), polyimide (glass), polyamide, acrylonitrite-butadiene-styrene block polymer (ABS), ceramic, Teflon and cyanate ester.

Here, too, a surprisingly quick coating was achieved after a 2 μm copper layer thickness.

Example 6

Like example 4 using all of the non-conductors listed in example 3, but additionally with so-called "rigid-flex circuits" which consist of epoxy / glass / polyamide and acrylic ether. Also using materials such as phenolic resin / paper (FR 2), epoxy / paper (FR 3), combination of epoxy / glass and epoxy / paper (CEM 1) with and without acrylic adhesive. After five minutes of electrolytic copper plating at 2 A / dm ² , all of the copper-clad materials indicated were 100% occupied. The edges of the samples had already grown optically after 30 seconds.

Example 7

Examples 3-6 were carried out both in diving, gushing and flooding.

The good results from before could be achieved in any case, even if ultrasound was used for cleaning / conditioning.

Example 8

The "pre-activation" (point 3) listed in Example 3 was replaced by a commercially available colloidal palladium / tin activator (pH = 1).

The results obtained are essentially the same; with the disadvantage of "entrainment of tin gel".

Example 9

Like example 8, but the "pre-activation" (point 3) is carried out in two steps:

1. Palladium activator (ionic), 1 min 40 ° C pH 12

do the washing up

2. Reduce 1 min 30 ° C The results are still good, analogous to the previous examples.

Claims

1. Process for the metallization of non-conductors, characterized by the process steps:

a) treatment of the non-conductor with a chelating agent and / or an ionogenic organic compound,

b) treatment with a solution containing noble metal optionally containing one or more reducing agents,

c) treatment with a manganate and / or permangant-containing solution,

d) treatment with a monomeric and / or oligomeric, acidic pyrrole solution,

e) electrolytic metallization.

2. The method according to claim 1, wherein the ionic organic compound is an N-methyl-N "-Vinyl-imidazolinium salt, N-methyl-N" -Vinylpyrrolidoniu salt, N-vinylimidazolium salt, N-butyl-N "-Allylbenzimidazoliumsalz, or whose homo- or copolymerized compounds polymerized via vinyl and / or allyl groups are used.

3. The method according to claim 1, wherein ethanolamine, triethanolamine, ethylenediaminetetraacetic acid (EDTA) or amino acids are used as chelating agents.

4. The method according to claim 1, wherein a palladium-containing solution is used as the noble metal-containing solution.

5. The method according to claim 1, wherein a solution containing noble metal containing an organic protective colloidal colloidal solution of the noble metal is used.

6. The method according to claim 5, wherein tin (II) compounds for

Stabilization of the colloidal precious metal-containing solution can be used.

7. The method according to at least one of claims 1-6 for metalizing circuit boards. _- •

8. The method according to at least one of claims 1-7, characterized gekennezichnet that these are operated in continuously operating horizontal horizontal plants.