EP0166327B1 - Process for manufacturing printed circuit boards - Google Patents

Abstract

1. Process for the manufacture of printed circuits by the wet-chemical metallizing of baseboards with the aid of organometallic activators, characterized in that a) the baseboards are activated, without prior etching, with a solution of 0.01-10 g/l of a complex compound of Pd, Au, Pt or Ag with a conjugated diene, alpha, beta unsaturated ketone, 4-cyclohexene-1,2-dicarboxylic anhydride or 4-cyclohexene-1,2-dicarboxylic imide, b) an electronically conductive metal coating with a layer thickness of 0.05-10 mu m and a stability to separation of at least 25 N/25 mm according to DIN 53 494 is applied to the boards activated in this way, by a wet chemical-electroless method or a combined wet chemical-electroless/electroplating method, and c) the baseboards metallized in this way, i. e. the so-called semi-finished products, are further processed in the customary manner to produce printed circuits.

Description

The invention relates to a wet chemical process for the production of printed circuit boards.

It is generally known that the deposition of adherent metal layers on the usual insulating base materials requires a complex pretreatment. For example, the base plates must first be provided with an adhesion promoter layer and then treated with oxidizing liquid, preferably chromosulfuric acid, before the plates prepared in this way are activated, masked and metallized in commercially available metallization baths with ionic or colloidal noble metal solutions.

Apart from the many levels of these methods, this technique has the disadvantage that chromium ions which have been introduced poison the baths irreversibly and that the printed circuit boards obtained have unsatisfactory electrical properties.

It has therefore already been proposed to activate the non-conductive surfaces of substrates, for example base carriers of printed circuit boards, without oxidative pretreatment with a solution or a lacquer of a noble metal complex compound for the subsequent chemical metallization (cf. e.g. DE-A 1 696 603 and DE- A 2 116 389) ..

However, these activation methods, which are gentle on the material, have so far not been able to establish themselves in practice, since they require relatively large amounts of activator and do not achieve the high pull-off strengths of the metal layers required in the electronics industry. For this reason, the addition of a resin or plastic to the activator solution as an adhesion promoter is recommended, at least in the first-mentioned patent publication.

• a) die Basisplatten ohne vorherige Ätzung mit einer Lösung von 0,01-10 g/I einer Komplexverbindung von Pd, Au, Pt oder Ag mit einem konjugierten Dien, a,ß-ungesättigten Keton 4-Cyclohexen-1,2-dicarbonsäureanhydrid oder 4-Cyclohexen-1,2-dicarbonsäureimid aktiviert,
• b) auf den so aktivierten Platten naßchemisch-stromlos oder kombiniert naßchemisch-stromlos/ galvanisch eine elektronisch leitfähige Metallauflage mit einer Schichtdicke von 0,05-10 µm und einer Abzugsfestigkeit nach DIN 53 494 von mindestens 25 N/25 mm aufbringt und
• c) die auf diese Weise metallisierten Basisplatten, die sog. Halbzeuge, in üblicher Weise zu Leiterplatten weiterverarbeitet.

It has now been found that these disadvantages can be avoided and semi-finished products for the production of high-quality printed circuit boards can be obtained in a simple manner if one

• a) the base plates without prior etching with a solution of 0.01-10 g / l of a complex compound of Pd, Au, Pt or Ag with a conjugated diene, a, β-unsaturated ketone 4-cyclohexene-1,2-dicarboxylic anhydride or 4-cyclohexene-1,2-dicarboximide activated,
• b) an electronically conductive metal coating with a layer thickness of 0.05-10 µm and a peel strength according to DIN 53 494 of at least 25 N / 25 mm is applied to the activated plates in this way, using a wet-chemical electroless or combined wet-chemical electroless / galvanic method, and
• c) the base plates metallized in this way, the so-called semi-finished products, are further processed in the usual way to printed circuit boards.

Compared to the known subtractive method, in which metal layers up to 70 μm thick have to be partially removed with the aid of etching solutions, the method according to the invention has the advantage that a metal layer with a thickness of only a maximum of 10 μm, preferably 0.1-7 , 5 µm or - particularly preferably 0.1-5.0 µm - must be etched out, which results in considerable material savings.

Compared to the "thin-film methods" for the production of printed circuit boards, which are also known and which are characterized by the lamination of galvanically produced thin-film layers, the new process is characterized by less work and improved mechanical and electrical properties of the metal layers.

Some of the activators required to carry out the new process are described in DE-A 3 148 280 and EPA 81 129 or are obtainable by processes known per se.

worin

• R, und R₄ C_l-C₂₀-Alkyl, vorzugsweise C,-C₆-Alkyl,
• R₂ und R₃ Wasserstoff oder C,-C₄-Alkyl, vorzugsweise Methyl bedeuten.
• Beispielhaft seien genannt : Mesityloxid, n-Buten-3-on-2, n-Hepten-3-on-2, n-Hexen-3-on-2, n-Decen-4-on-3, 5-Chlor-penten-3-on-2, Ethylvinylketon, 3-Methyl-octen-5-on-4, 3-Methyl-penten-3-on-2, 7-Metho- xy-hepten-3-on-2.

Suitable unsaturated ketones for the production of the activators are those of the formula

wherein

• R, and R _{4 are} C ₁ -C ₂₀ -alkyl, preferably C, -C ₆ -alkyl,
• R ₂ and R _{3 are} hydrogen or C, -C ₄ alkyl, preferably methyl.
• Examples include: mesityl oxide, n-buten-3-one-2, n-hepten-3-one-2, n-hexen-3-one-2, n-decen-4-one-3,5-chloro penten-3-one-2, ethyl vinyl ketone, 3-methyl-octen-5-one-4, 3-methyl-penten-3-one-2, 7-methoxy-hepten-3-one-2.

The palladium complexes are particularly preferred.

The novel process is advantageously carried out in such a way that base materials with the above. wetted organometallic compounds. This can be done primarily by spraying with a volatile organic solution of the activators mentioned or by dipping into these media.

Chlorinated hydrocarbons such as HCCI ₃ , CCl ₄ , CH ₂ CI ₂ and CICH = CCI ₂ are preferred as solvents. Alcohols such as C ₂ H ₅ OH and CH ₃ 0H or their mixtures with one another into consideration.

The base materials treated in this way are then, if necessary swollen in a solvent, then sensitized and metallized over the entire area in a reductive metallization bath.

If necessary, the metal coating thus obtained is galvanically reinforced up to a maximum total thickness of 10 µm.

Then the metallized base material, also called “semi-finished product”, is partially provided with a mask.

In most cases, “resist layers” (photoresists, photoresists), namely “negative resists” or “positive resists” are used to cover the semi-finished products. They are generally known (see, for example, Günther Hermann, “Printed Circuit Boards, Manufacturing and Pretreatment •, pp. 98-103 and 125-127).

In the first case, the unexposed parts are removed with a suitable solvent after the exposure, in the second case the exposed parts. A number of special resist systems can be used to produce reliefs for electronics or for microelectronics. In this context, the resist systems curable with the aid of UV radiation, electron radiation and laser radiation should be mentioned (cf. DE-A 2 007 267, DE-A 2 454 879 and DE-A 2 507 874).

Conventional organic solvents in which the prepolymer of the lacquer layers is readily soluble are suitable for removing the non-crosslinked parts of the resist layer.

The relief mask can also be applied by screen printing, coating or stamping.

Suitable substrates for the process according to the invention are plates, preferably plates made of glass fiber and glass mat reinforced epoxy resins provided with standard holes (see, for example, Kunststoff Handbuch, Prof. R. Vieweg, XI, pp. 180-246, Carl Hanser Verlag, Munich (1971)) , fluorine-containing polymers (see, for example, reference p. 673-674) such as PTFE (polytetrafluoroethylene), thermosetting plastics such as phenol-formalin and / or melamine resins (see, for example, Prof. R. Vieweg "Plastics Manual" X, p. 19-59 and 63-128), polypropylene, polyethylene, ABS (acrylonitrile butadiene styrene) mixed or graft copolymers and polycondensates (e.g. polycarbonates, aromatic and / or aliphatic polyamides, polyesters, aromatic and / or aliphatic polyamides or Polyamide imides and their mixture or cocondensates).

In individual cases, the polymer plates must be swollen with a suitable swelling agent before metallization.

For the treatment of plates based on polyamide condensates, for example, solutions of a mixture of halides of elements of the 1st and / or 2nd main group of the periodic table with salts of weak inorganic bases and strong inorganic acids are used.

Suitable halides of elements of the 1st and 2nd main group are in particular the chlorides; LiCl, BeCl ₂ , MgCl ₂ and CaCl ₂ are preferred.

Suitable salts of weak bases and strong acids are sulfates, nitrates and especially chlorides of metals of the 3rd and 4th main and subgroups as well as base metals of the 6th-8th Subgroup. FeCl _2, FEC1 _3, TiCl _3, TiCl _4, BCI ₃ and in particular AICI ₃ are preferred.

Suitable swelling agents and solvents are those as described in conventional manuals on polyamides (see, for example, “Die Polyamide von Hopff. Müller, Wegner, Springer-Verlag (1954), and“ Polymer Handbook ”by Brandrup et al. New York, Volume IV (1975) and «Vieweg / Müller Plastic Handbook; Volume IV (1966)). Examples include: low aliphatic and araliphatic alcohols, such as. B. methanol, ethanol, isopropanol, n-propanol, n-butanol, benzyl alcohol and phenylethyl alcohol. Methanol is particularly preferred. Dimethyl sulfoxide and amide group-containing solvents such as formamide and dimethylformamide are also suitable. Mixtures of these solvents can of course also be used.

A particularly preferred swelling agent system is a solution of CaCl ₂ / AICI ₃ mixture in methanol.

If desired, conventional polyamide plasticizers (0.2-10% by weight or 0.5-5% by weight, based on the total amount of liquid) can also be added. Examples include benzenesulfonic acid monoethylamide, p-toluenesulfonic acid amide, dioxide diphenyl sulfone and dibenzyl alcohol.

According to a preferred variant of the method, the “activation” and “acquiring” operations can be combined by dissolving the activator in the swelling agent and using this system.

After the solvent treatment the adhering solvent is removed from the plates.

This is generally done by evaporation, possibly under reduced pressure. Higher-boiling solvents are expediently removed by extraction or rinsing with low-boiling solvents.

If fluoropolymers are used as substrates, this variant is preferably carried out by immersing these polymers in an organic, preferably anhydrous, solution such as THF (tetrahydrofuran), benzene and toluene, which additionally contains an alkali organic compound with a solitary, contains capable of forming a pair of electrons capable of carbanion or carbcation. In this context, reference should be made to the references “ND Scott et al. : At the. Soc. 58, 2443 (1936); ND Scott: USP 2,181,771; M. Szwar: Nature 178, 1168 (1956): M. Szwarc: Am. Soc. 78, 2656 (1956). Where naphthalene sodium, naphthalene lithium, benzollite hium, benzene sodium, biphenyl, triphenyl and butyl lithium or sodium are particularly preferred. The concentration of the alkali organic compounds should be 0.01 to 250, preferably 2.5-100, particularly preferably 5-75 g per liter of solvent.

The thermosets based on phenolic, epoxy and melamine resins, which can also be used to produce base materials according to the invention, can of course be coated with an adhesion promoter (see, for example, G. Hermann, printed circuit boards, manufacture and preparation. Pp. 164-168, Eugen G. Lenze Verlag , Sauigau / Württ. (1978)), which contains a rubber-elastic component. Likewise, after their activity to increase the peel strength of the metal layer deposited in the last step, they can be dissolved in solvents or swelling agents customary for the ABS polymers (see, for example, “Polymer Handbook Brandrup et al. New York, Volume IV (1975)) or in oxidizing media are treated.

The pretreated and activated base plates have to be sensitized by reduction. The reducing agents customary in electroplating, such as hydrazine hydrate, formaldehyde, hypophosphite or boranes, can preferably be used for this purpose. Of course, other reducing agents are also possible. The reduction is preferably carried out in aqueous solution. However, other solvents such as alcohols, ethers, hydrocarbons can also be used. Of course, suspensions or slurries of the reducing agents can also be used.

The surfaces sensitized in this way can be used directly for electroless metallization. However, it may also be necessary to rinse the surface of the reducing agent residues.

A very particularly preferred embodiment of the method according to the invention consists in that the reduction in the metallization bath is carried out immediately with the reducing agent of the electroless metallization. This version represents a simplification of the electroless metallization that was previously not possible.

This embodiment is very particularly suitable for the nickel baths containing amine borane or copper baths containing formalin, which are preferably used.

Commercially available baths of nickel salts, cobalt salts, copper salts, gold and silver salts or mixtures thereof are suitable as metallization baths which can be used in the process according to the invention.

• Ni, Co, Cu, Ag, Al, Cr und Au. Bevorzugt ist Cu.

The following metals are suitable for galvanic reinforcement:

• Ni, Co, Cu, Ag, Al, Cr and Au. Cu is preferred.

• Die Halbzeugmaterialien zur Herstellung von Leiterplatten sollen folgende Eigenschaften aufweisen :
  • 1. Sie sollen im aktivierten Zustand an der Luft gegenüber Feuchtigkeit stabil sein.
  • 2. Ihre Aktivatorauflage soll nicht während des Aufbringens bzw. des Entwickelns von Fotoresistauflagen von der Oberfläche entfernbar oder gar desaktivierbar sein.
  • 3. Ihre Aktivatorauflage soll nicht während einer Quell- oder Oxidantieneinwirkung von der Oberfläche entfernt bzw. desaktiviert werden.
  • 4. Ebenso darf die Reliefauflage während des Quell- oder Abbauvorganges von der Materialoberfläche nicht abgeschwemmt werden.
  • 5. Die Abzugsfestigkeit der Metallauflage nach DIN 53 494 soll mindestens 25, vorzugsweise 50 N/25 mm betragen.
  • 6. Bei der Sensibilisierung bzw. Metallisierung dürfen keine Liganden freiwerden, die die Metallisierung- oder Sensibilisierungsbäder vergiften.

Semi-finished products, that is to say polymer plates provided with an electroless, wet-chemical thin-layer metal coating on any basis, based on polyamides and fluoropolymers, have not previously been described in the literature and are therefore also an object of the invention:

• The semi-finished materials for the production of printed circuit boards should have the following properties:
  • 1. When activated, they should be stable to moisture in the air.
  • 2. Your activator pad should not be removable from the surface or even deactivated during the application or development of photoresist pads.
  • 3. Your activator pad should not be removed or deactivated from the surface during exposure to swelling or oxidizing agents.
  • 4. Likewise, the relief overlay must not be washed away from the material surface during the swelling or dismantling process.
  • 5. The peel strength of the metal support according to DIN 53 494 should be at least 25, preferably 50 N / 25 mm.
  • 6. During the sensitization or metallization, no ligands must be released which poison the metallization or sensitization baths.

The further processing of these semi-finished products into printed circuit boards by partial masking, if necessary galvanic reinforcement up to 50 µm and removal of the unnecessary metal areas with suitable etching solutions is carried out using customary methods.

There are basically two options for further processing.

The first is characterized in that the non-masked areas on the semi-finished product are removed with the etching solution. In this way, printed circuit boards with a relatively thin metal coating, namely a maximum of 10 µm, are obtained.

In contrast, the preferred procedure consists in galvanically strengthening the non-masked areas up to a maximum of 50 J.l.m and then optionally protecting them with a tin layer before the mask and the underlying thin layer layer are removed with the aid of an etching solution.

Of course, the metal layers deposited using said method can also be developed in a grid-like manner using the differential etching method.

example 1

enthält, 5 Minuten bei RT behandelt. Anschließend wird die Platte in einem Bad, bestehend aus

5 Min. bei RT sensibilisiert, mit destilliertem Wasser gespült und dann in einem handelsüblichen Verkupferungsbad bei 30 °C bis zu einer Metallauflage von ca. 1 µm verkupfert.A 200 x 200 x 1 mm thick glass fiber reinforced (30%) and provided with standard holes Plastic plate made of polyamide-6 is activated for 5 minutes in a solution of 1 g of 4-cyclohexene-1,2-dicarboxylic acid anhydride palladium (11) chloride in 1 1 CH ₂ Cl ₂ at room temperature (RT), dried and in a bath which

contains, treated for 5 minutes at RT. The plate is then made up in a bath

Sensitized for 5 min at RT, rinsed with distilled water and then copper-plated in a commercially available copper plating bath at 30 ° C. up to a metal layer of approx. 1 µm.

The galvanic reinforcement of this layer up to a total layer thickness of 5 µm takes place in a conventional galvanizing bath.

besteht, 10 Min. nachbehandelt.The thin-layer plate produced in this way is covered with the aid of a screen printing varnish based on a styrene-butadiene copolymer, which has free comb-shaped webs of about 500 μm in width, and then in a bath which consists of

exists, treated for 10 minutes.

A plated-through circuit board with 500 μm wide and 4.0 μm thick conductor tracks is obtained. The metal coating adheres so well to the substrate surface that it cannot be removed from the polymer surface despite a 1-minute post-treatment at 265 ° C in a drying cabinet.

Example 2

A 200 x 200 x 1 mm commercial rubber-grafted polyamide 6 plate is provided with 0.2 mm holes in a bath of 1 liter. CH ₂ C1 ₂ and 0.9 g mesityl oxide-palladium chloride activated in the course of 4 minutes at 18 ° C., dried, in a bath

bei 20 °C 5 Minuten behandelt, gemäß Beispiel 1 sensibilisiert und dann in einem handelsüblichen Verkupferungsbad auf dem chemischen Wege verkupfert.

treated at 20 ° C for 5 minutes, sensitized according to Example 1 and then copper-plated by chemical means in a commercially available copper plating bath.

After about a few minutes, the sample surface turns dark and after about 30 minutes a good electrically conductive Cu layer is deposited. This is galvanically reinforced to approximately 7.5 µm.

bildmäßig entwickelt.The thin-layer printed circuit board produced in this way is sprayed with a UV-curable lacquer based on oligomeric 1,4-polyisoprene (approx. 5% by weight in xylene) from Agfa Gevaert AG, Leverkusen) and then dried. After a week, the surface of the semi-finished product is covered with a photo mask and partially crosslinked with the help of UV radiation. The non-crosslinked prepolymer part is removed from the test specimen in methanol (very pure) after the mask has been removed. The thin-layer plate is then removed in a bath at 25 ° C

developed pictorially.

A plated-through circuit board with 40 μm wide and 7.5 μm thick conductor tracks is obtained. The peel strength of the metal pad measured according to DIN 53 494 is approx. 60 N / 25 mm and passes the 15 second solder bath test at 255 ° C.

angesetzt wird, 5 Min. vorbehandelt.A 200 x 200 x 1 mm large commercially available polytetrafluoroethylene film is provided with standard holes and in a solution which consists of

is prepared, pretreated for 5 minutes.

The plate is then washed neutral with methanol and then in a bath which is made of

0.9 g n-3-hepten-2-one palladium chloride

besteht bei RT 5 Min. sensibilisiert, gewaschen und dann in einem handelsüblichen Vernickelungsbad vernickelt.1,000 ml CC1 ₂ = CHCI, treated at 30 ° C for 6 minutes and then dried. The plate activated in this way is in a bath which is made of

exists at RT for 5 min. sensitized, washed and then nickel-plated in a standard nickel plating bath.

After about two minutes, the test specimen turns silver-gray and after about 20 minutes an electrically highly conductive Ni coating is deposited, which is reinforced to 3.5 µm with galvanic silver.

The thin-layer plate produced in this way is coated with a UV-curable resist lacquer, dried and then covered with a photomask or partially crosslinked with the aid of UV radiation. The non-crosslinked prepolymer portion is removed from the base material in a commercially available developer solution after removal of the mask. The plate is then post-treated in the metal etching solution specified in Example 1.

You get a plated-through circuit board. The metal coating adheres to the polymer surface so well that it passes the temperature according to DIN 53 436. This plate can be easily soldered in a commercial tin soldering bath at elevated temperature (250-260 ° C) in the course of a few minutes.

Example 4

A 200 x 300 mm aromatic polyimide film (Kapton ^(R) ) is provided with holes according to Example 1, in a solution which consists of 1.0 g of 4-cyclohexene-1,2-dicarboximide palladium chloride and 1 liter. CH ₂ C1 ₂ is activated, sensitized according to Example 1, metallized and then the metal coating developed according to Example 2.

A printed circuit board is obtained, the metal coating of which adheres so well to the substrate surface that it cannot be removed from the polymer surface despite a 1-minute aftertreatment in a commercial solder bath at 250 ° C.

Example 5

A 100 x 100 x 1 mm 40% mineral filler-reinforced polymer plate made of polyamide-6 is made in a bath from 0.8 g of 4-cyclohexene-1,2-dicarboxylic acid imide-palladium (II) chloride, 1 500 ml of methanol, 120 g CaC1 ₂ and 3 g AICI ₃ adhesive activated at 30 ° C for 5 minutes. The plate is then sensitized in a bath consisting of 1 200 ml of ethanol, 24 ml of NH ₃ solution (25%) and 500 ml of 2N-DMAB (dimethylamine borane) solution, washed for 5 minutes, in a commercially available wet-chemical copper plating bath an approx. 5 µm thick copper layer and then coated with a UV-curable resist film from BASF AG. Now this semi-finished product surface is covered with a photomask, which has free, continuous paths of approx. 200 µm, and partially crosslinked with the aid of UV radiation. The non-crosslinked prepolymer portion is removed from the base material in a commercially available developer solution after removal of the mask. The free metal surface is then galvanically coated with a 35 µm thick copper layer and then with a 2 µm thick tin layer. Now the polymer-metal composite in methylene chloride is freed from the polymeric resist coating and 35 minutes in a Cu etching solution consisting of 100 ml HCl (37%), 30 ml H ₂ 0 ₂ (40%) and 1,000 ml H ₂ 0 treated.

An electrical circuit board is obtained with continuous conductor tracks 200 μm wide and approx. 42 μm thick, consisting of approx. 5 ₄ m chemical and approx. 35 µm galvanic copper or approx. 1 µm galvanic tin. The metal coating adheres so well to the substrate surface that it cannot be removed from the polymer surface despite a two-hour aftertreatment at 160 ° C.

Example 6 4-cyclohexene-1,2-dicarboximide palladium (II) chloride

10 g of 4-cyclohexene-1,2-dicarboximide are dissolved in five times the amount of dimethylformamide, and the equimolar amount of acetonitrile palladium dichloride is added at 45 ° C. in the course of 3 hours. DMF and acetonitrile are distilled off at 45 ° C / 25 mbar. A yellow-brownish solid with a melting point of 102 ° C. is obtained in 95% yield.

Example 7

A perforated polyamide plate is activated in accordance with Example 5 and a UV-curable resist film (LN ^® Nylotron BASF AG) coated. Now the substrate surface is covered with a mask, partially cross-linked with the aid of UV radiation. The non-crosslinked prepolymer part is removed from the plate surface after removal of the mask by treatment with 1,1,1-trichloroethane. The test specimen according to Example 1 is then swollen in a methanolic solution, sensitized, rinsed with distilled water and then partially copper-coated in a commercially available copper plating bath at 60 ° C. up to a metal coating of approximately 17.5 μm.

A finished printed circuit board is obtained, the copper layer of which adheres so well to the surface of the board that it cannot be removed from the board surface despite a one-day post-heating at 140 ° C.

Claims (3)

1. Process for the manufacture of printed circuits by the wet-chemical metallizing of baseboards with the aid of organometallic activators, characterized in that

a) the baseboards are activated, without prior etching, with a solution of 0.01-10 g/I of a complex compound of Pd, Au, Pt or Ag with a conjugated diene, α,β unsaturated ketone, 4-cyclohexene-1,2-dicarboxylic anhydride or 4-cyclohexene-1,2-dicarboxylic imide,

b) an electronically conductive metal coating with a layer thickness of 0.05-10 µm and a stability to separation of at least 25 N/25 mm according to DIN 53 494 is applied to the boards activated in this way, by a wet chemical-electroless method or a combined wet chemical-electroless/electroplating method, and

c) the baseboards metallized in this way, i.e. the so-called semi-finished products, are further processed in the customary manner to produce printed circuits.

2. Process according to Claim 1, characterized in that the activator system also contains a swelling agent for the baseboards.

3. Process according to Claim 1 or 2, characterized in that the swelling agent is a solution of CaCI₂/AICI₃ in methanol.