US3804638A - Electroless deposition of ductile copper - Google Patents

Abstract

A bath for electroless copper-plating containing a soluble copper salt, one or more complexing agents, formaldehyde and as an addition, which gives copper a satisfactory colour and makes it ductile also in case of comparatively large layer thicknesses, a polyalkylene oxidic compound including at least four alkylene oxide groups. The bath does not contain cyanide, nitrile or a metal compound of, for example, V, As or Sb.

Description

United States Patent 1191 Jonker et a].

[ 1 ELECTROLESS DEPOSITION OF DUCTILE COPPER [75] Inventors: Hendrik Jonker; Arian Molenaar;

Eise Bernard Geertsema, all of Emmasingel, Eindhoven,

Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

[22] Filed: Apr. 6, 1972 [21] Appl. No.: 241,806

{30} Foreign Application Priority Data Oct. 16, 1969 Netherlands 6915718 [52] US. Cl. 106/1, 117/130 E, i17/47 R,

117/54, 117/160 R [51 Int. Cl. C23c 3/02 [58} Field of Search 106/1; 117/130E {56} References Cited UNlTED STATES PATENTS 3,075,856 1/1963 Lukes 106/1 X Apr. I6, 1974 3,300,335 1/1967 l-lorvath et a1 106/1 X 3,472,664 10/1969 Bastenbeck et a1 106/1 3,485,643 12/1969 Zeblisky et a1. 106/1 3,515,563 6/1970 Hodoley et a1. 106/1 Primary Examiner-Ralph S. Kendall Attorney, Agent, or FirmNorman N. Spain; Frank R. Trifari 5 7] ABSTRACT 9 Claims, 1 Drawing Figure (mail/ INVENTORS HENDRIK JONKER ARIAN MOLENAAR SE B. GEERTS El I A BY 1W/ ELECTROLESS DEPOSITION OF DUCTILE COPPER This is a continuation, of application Ser. No. 78,?40, filed Oct. 7, 1970 now abandoned.

The invention relates to an alkaline aqueous electroless copper-plating bath and provides simplified methods of depositing ductile copper.

in this connection electroless copper-plating is understood to mean the deposition by chemical reduction of an adherent copper layer on a suitable surface in the absence of an external source of electricity. Such a copper-plating method is used, for example, on a large scale in the manufacture of printed circuits, conducting coatings which are subsequently to be further coated electrically, and for decorative purposes.

Different electroless copper-plating baths are already known. Such aqueous solutions generally contain cupric ions, formaldehyde, an alkali hydroxide and a complexing agent which prevents the cupric ions from being deposited in an alkaline medium. The copper deposition with the aid of such a bath is effected by reduction of cupric ions to copper by the formaldehyde, which reaction is initiated by a catalytic surface, for example, a catalytic metal or a synthetic resin which has been made catalytic (activated).

The known electroless copper-plating baths have a number of drawbacks. For example, the appearance of electroless deposited copper often greatly deviates from that of metallic copper. it is then, for example, not metallically bright but dull and has a dirty dark colour and a great brittleness, a comparatively small specific electrical conductance and a poor solderability. Among the known solutions which have a comparatively high deposition rate especially at the beginning the quality of the deposition is generally poor and it is characteristic that the deposition rate in many cases is rapidly reduced and sometimes decreases to zero. Consequentiy slow and hence more stable copper-plating solutions are generally used with the aid of which a basic layer having a thickness of 0.! to approximately 0.25 porn is deposited, for example, within l5 minutes, which layer is subsequently electrolytically copperplated to the desired thickness. A layer having a thickness in the order of 25-50 punt is generally desired and the electrolytic copper-plating process involves a considerable investment and a number of additional operations.

Apart from this fact it is generally difficult to use an electrolytical coppenplating process when copper is to be deposited in accordance with a pattern whose parts are not uninterruptedly coherent for example, in addi' tive methods of manufacturing printed circuits). A drawback of electrolytic depositions is also that these depositions often differ in thickness as a result of an irregular current density distribution. The commerciaily available electroless copper-plating solutions are generally of the slow type and are not suitable to deposit in an economic manner thick, ductile, adherent copper layers which are free from blisters. These solutions also generally have the unpleasant property that the deposition rate, being slow as it is, is reduced during deposition.

One of the little known solutions for electroless copper-plating by which a layer of eminent, ductile copper up to a thickness of approximately 25 pum can be deposited within 24 hours contains an inorganic cyanide andior an organic nitrile (U.S. Pat. No. 3,095,309). According to a further proposal, for example, vanadium pentoxide, sodium arsenite or potassium antimony tartrate is added instead of cyanide and/or nitrile to copper-plating solutions so as to effect the deposition of ductile copper (U.S. Pat. No. 3,310,430). All mentioned additions have the drawback that they have a highly toxic effect on the copper deposition and in certain cases the activity of a solution may stop completely and substantially instantaneously in the presence of several parts per million of the relevant compound. As a result the dosage must be very accurate so that also inspection of the deposition process requires much attention. Finally a number of the said compounds are extremely toxic.

A novel method of electroless copper-plating has recently become known (U.S. Pat. No. 3,329,512) whose major object is to deposit copper up to the thickness of 25 gum or more at a rate of at least 6 uum per hour and preferably more. To this end at least a great part of the complexing agent for cupric ions in the copper-plating solution consists of one or more hydroxyalkylsubstituted tertiary amines, which solution also contains a colloidal soluble non-reactive polymer chosen from the group of cellulose ethers, hydroxyethyl starch, polyvinylalcohol, polyvinylpyrrolidone, gelatin, peptones, polyamides and polyacrylarnides. The polymer addition acts as a brightnening agent. The appearance of the copper layers which are deposited with the aid of such solutions is very satisfactory indeed, but the ductility of the layers is generally marginal and even insufficient when the relevant solutions are used for the manufacture of printed circuits in accordance with an additive method.

It is an object of the present invention to provide a bath for electroless deposition of copper up to the desired thickness in such a manner that the ductility of satisfactory electrolytic copper is approximated and that the above-mentioned drawbacks of the known baths and methods are obviated, and by which method smooth, brightly red, reasonably ductile, comparatively thick copper layers can be deposited in an economic manner at a rate of approximately 5 pum per hour or more.

The ductility may be determined by partially loosening the deposited copper layer from the substrate and bending it in one direction over folding it and bending it back in its original position whereafter the fold is flattened under pressure. This completes one band. The operations are repeated until the layer breaks and thus it is possible to express the ductility in the number of bends which the layer can stand. For obtaining comparable results it is desirable to perform the measurements on copper layers of comparable layer thickness, for example, 15-20 uum.

The starting point for the experiment which led to the present invention was that the ductility should be at least two bends with a view to versatile unability. This experiment showed that the ductility of electroless deposited copper depends on the rate of deposition which follows from the following Table which applies for a bath temperature of 50C.

Bath composition (moles/litre) Layer thicknessutrnl Average depo- Ductility CuSo,,5H,0 EDTAHNa) NaOH Na,CO, HCHO after it hours sition rate (bends) m/hour) 0.008 0.009 0.10 0.18 20 pm in [3 hours 1.5 S 7 0.014 0.0IS 0.10 0.10 0.18 20 pm in ID hours 2.0 2% 0,020 0.025 0.10 0.10 018 25 pm in 6%hours 3.8 ii

I EDTA [4 Na) in the tctraodium salt of ethylenediaminctetnlcetic acid Furthermore it was found that 20 uum of copper l um/hour) having a ductility of two to three bends could be deposited at a comparatively high temperature (75 C) within two hours from a fairly unsta ble bath of the following composition:

CuSO,, EH 0 0.02 mol/litre EDTA (4Na) 0.02 do. NaOH 0.I() do. HCHO (H8 do.

Goldie (Plating, Nov. 1964) was able to deposit 1.54 mg Cu/sq.cm (approximately 0.85 yum/hour) at 20C within 2 hours from a bath of the following composition:

CuSQ H,0 0.04 mol/litre Potassiumsodiumtartrate 0J8 mol/litre NIOH O.l75 mol/litre HCHO 0.13 mol/litre It was found that copper deposited from such a bath at this temperature did not satisfy our condition of ductility. The critical rate at which reasonably ductile copper (at least two bends) can be deposited was thus found to be greater as the temperature of the bath increased.

During the experiment which led to the present invention the starting point was chosen to be the assumption that the improvement in ductility which may be brought about by an addition of, for example, inorganic cyanide, organic nitrile, vanadium pentoxide, sodium arsenite or potassium antimony tartrate should be ascribed to the reduction of the rate of deposition caused by such an addition.

However it was stated that compounds which contain bivalent sulphur such as thiourea and 2-mercaptobenzothiazole which are sometimes used to enhance the stability of copper-plating solutions, although they reduce the rate of the copper deposition already at very small quantities, generally do not enhance the ductility but rather the contrary. The inventors also found that certain cationic surface-active compounds such as cetylpyridiniumchloride and cationic polyethylenimine and the anionic compound heptadecylbenzimidazole monosulphate (Na-salt) neither enhance the ductility although they also reduce the deposition rate to a great extent.

Unlike cyanide and nitrile, all mentioned additions have a detrimental influence on the appearance of the deposited copper.

It was surprisingly found that many polyalkylene oxidic (polyalkoxy) compounds used in electroless copper-plating solutions have the property that they both reduce the deposition rate of copper and enhance the ductility and the appearance of the deposition, while in addition they tend to shift the limit of suitable ductility to faster deposition rates. In this respect it is important that none of the essential constituents of the solutions is present in a concentration which exceeds a certain limit. However, many variations are possible within the admitted regions of concentration.

The aqueous alkaline electroless copper-plating bath according to the invention for metallizing with ductile copper and containing a soluble copper salt, one or more complexing agents and formaldehyde is characterized in that it is free from an inorganic cyanide, an organic nitrile or a compound of one of the following elements: molybdenum, niobium, tungsten, rhenium, vanadium, arsenic, antimony, bismuth, actinium, lanthanium and the rare earths and that it contains as its essential constituents 0.01 0.10 mol of a copper salt soluble in water, a total of 0.01 0.80 mol of one or more complexing agents which prevent cupric ions from being deposited from the alkaline solution, 0.05 0.50 mol alkalihydroxide (pH approximately: ll l3.5), 0.01 0.35 mol formaldehyde or a compound producing a formaldehyde and to enhance the ductility of the depositing copper an effective concentration ofa soluble, non-ionic or ionic polyalkylene oxidic compound either or not constituting micelles which contain at least four alkylene oxide (alkoxy) groups.

An effective concentration of the polyalkylene oxidic compound is understood to mean a concentration which enhances the ductility and when insufficient ductile copper is deposited from the solution without the active compound is at least such that a ductility of at least two bends is obtained. Also, an effective copper concentration substantially always enhances the colour and the smoothness of the deposition and often reduces the number of blisters formed in the surface of the deposited copper and enhances the adhesion of the deposited layer.

Although the deposition rate of copper is generally reduced due to the presence of a polyalkylene oxidic compound according to the invention, it has been found that dependent on the concentrations of the essential constitutents of the copper-plating solution it is not always possible to reduce it to the critical rate at which copper is deposited at a ductility of two bends. For this reason a maximum but still suitable limit concentration is indicated above for each essential constituent of the solution. The minium limit concentrations are determined by the requirement that copper must be deposited at a rate which is still acceptable for practical use. Maximum and still acceptable concentrations of the other constituents are associated with each maximum limit concentration of an essential constituent, which concentrations are generally lower than the mentioned maximum limit concentrations of said constituents. Thus this means that when the limit concentration of one of the constituents is exceeded in a copper plating solution, the technical effect of the invention can no longer be realized to its full extent. This does not mean that this is indeed the case in a bath in which all concentrations correspond to the limit concentrations. It has been found that the critical deposition rate is also slightly influenced by the nature of the complexing agent for cupric ions so that a general critical rate for all baths containing polyalkylene oxidic compounds cannot be given. On the other hand, as already noted, the critical rate increases with the operating temperature of the copper-plating soiution.

It is to be noted that electroless copper-plating baths of the previously described type are known from US. Pat. No. 3,257,215, which baths contain a cyanide compound and a rnercapto compound. it is recommended to add a wetting agent to the bath, the specification mentioning a few agents which satisfy the definition according to the invention. However, it was found that addition of such a wetting agent to such a cyanidecontaining bath does not provide any improvement with regard to ductility as compared with the corresponding bath without a wetting agent. These known baths have the drawbacks already referred to.

A large number of suitable polyalkylene oxidic compounds is defined by the following general formula R(OC H,) (OCJi h, (OCQ-IJ R with a+b+c a 4( For the polyaikylene glycols not constituting micelles there applies that R, H and R,=01-l. For the polyethylene glycols b is equal to zero and the formula changes into H(OC H,) OH. For the polypropylene glycols a and c are both zero and n 3 H(OC l-l OH and for the polybutylene glycols both a and c are likewise zero and n 4 H(OC H OH.

Polyethylene glycols are satisfactorily soluble in water even when they have a high molecular weight. Thus they are very much suitabie for use within the scope of the present invention. Even a compound having a molecular weight of 500,000 and a c 1,100 is found to be still effective. When the molecular weight of polypropylene and polybutylene glycols increases, the solubility decreases. When the compounds are completely insoluble in the copper-plating solution, they are unsuitable for the method according to the invention. Compounds which are interesting with a view to their suitability are block polymers with a 1, b 1, and c 1 and n 3. These are compounds which consist of one more hydrophobic blocit of propylene oxide (propoxy) groups flanked by hydrophilic blocks of ethylene oxide (ethoxy) groups. Such compounds are commercially available under the name of Pluronics (Wyandotte Chemicals Corp.) in a great variety of compositions and molecular weights. It has been found that polyalkylene oxidic compounds which contain approximately 13 or more alkylene oxide (alkoxy) groups are active within a very wide range of concentrations when they are used in copper-plating solutions which are composed in conformity with the concentration requirements formulated hereinbefore. This may be concluded from the following embodiments which also ll polybutadieneacrylonitrile and cresoi resin which is provided on hard paper was locally activated by a photochemical process for the electroless copper deposition. This activation was performed as follows. Firstly the layer was immersed for a short period in a photosensitive solution of the following composition:

0.l0 mol orthomethoxybenzenediazosulphonate (Mg salt) 0.017 moi cadmium lactate 0.017 mol calcium lactate 0.017 mol lactic acid 10 gms Lissapol N deionized water up to l litre.

The pH of the solution was set at 4. The adherent liquid layer was dried with the aid ofa stream of cold air. The photosensitive layer was subsequently exposed behind a negative of fairly broad lines for 1 minute with the aid of a reprographic mercury vapour lamp (type HPR 150 W) which was at a distance of 42 cms from the negative. Subsequently the exposed layer was treated with a solution containing 0.075 mol mercurous nitrate 0.01 mol silver nitrate 0.15 mol nitric acid deionized water up to 1 litre.

The latent image formed consisting of metal nuclei, was slightly intensified with silver by treating it for 1 1/2 minutes with a solution comprising 0.01 mol silver nitrate 0.025 mol metol 0.10 citric acid deionized water up to 1 litre.

The weak image thus obtained consisting of catalytic silver nuclei was finally electroless copper-plated in a copper-plating solution of the composition:

0.028 moi copper sulphate (5 H O) 0.030 mol ethylenediaminetetraacetate (4 Na) 0.13 mol formaldehyde 0.10 mol sodium hydroxide J: mol polyethylene glycol water up to 1 litre. Copper layers of approximately 20 pm thickness were grown at a bath temperature of C on a number of substrates activated in the manner described. Without the addition of polyethylene glycol (x 0) the deposition rate was approximately 9 pm per hour. In that case nonductile copper k bend) was deposited.

By varying x the smallest effective concentration was determined for a series of polyethylene glycols having an increasing number of ethoxy groups. The compounds used are gathered in Table I.

lustrate the essence of the method according to the present invention.

EXAMPLE 1 An adhesive layer roughened with chromic acid sulphuric acid and based on a mixture of These minimum effective concentrations c are plotted in FIG. I as a function of the number of ethoxy groups n. The curve through the experimental points separates a region of satisfactory ductile copper from a region of non-satisfactory, non-ductile copper. If copper having a ductility of at least 2 bends is to be deposited, approximately 0.l mol per litre of the compounds including fewer than 8 9 ethoxy groups is to be added. For the compounds having more ethoxy groups much smaller concentrations may be sufficient. Nevertheless it is recommended to use a concentration which is slightly higher than the limit concentration. In that case ductilities of 3 8 bends may be obtained. The ductile copper was deposited in these cases at a rate in the order of I um per hour. It had a better metallic appearance and a slighter oxidation sensitivity than the non-ductile copper deposited from baths containing too little polyethylene glycol. It is to be noted that the method and extent of activating the substrate as well as the composially non-ionic and are eminently suitable for use within the scope of the present invention.

When R is a paraffin tail such as, for example, a lauryl, cetyl, stearyl, myristyl or oleyl group, then ethoxyl ated fatty alcohols, or more correctly expressed, an

ether of a fatty alcohol and a polyethylene glycol are concerned: C,,,H,, (OC,H OH. The alkyl group may alternatively be branched. Numerous active surface-active compounds of this type are commercially available such as, for example:

tion of the copper-plating solution within the indicated concentration ranges quantitatively exert some influence on the minimum effective concentration ofa poly- Fmbmfabm ethylene glycol, although this does not lead to a different li i inqage- Brij (series compounds) Atlas Chemical lnd.

EXAMPLE [I Empilan K (serie) Marchon Products Ltd.

Using substrates which were activated in the manner Emulgi gi described with reference to Example I for the electroless copper deposition, copper layers of approximately "enkel lmemalional 2O M thlcknss were g at a n tempera-tyre Ethosperse La (serie) Glyco Chemicals, Inc. C whlle using copper-plating solutions contammg the following constituents, Lipal CSA (serie) Drew Chemical Corp.

LA (do) 0.028 mol copper sulphate (5 H O) MA (do.) 0.030 mol ethylenediaminetetraacetate (4 Na) (do-l 0.10 mol sodium hydroxide 3O Lam (5cm) Chcmy 0.13 mol formaldehyde Lubml AL (mic) y percent welght of polyalkylene glycol Peregal 0 General Aniline 81 Film Corp. water up to l litre. The polyalkylene glycols used and the ductilities of the 3 32'3" wyandme Chemicals copper layers deposited therewith are gathered in 35 RA g, Table 2. All compounds with the exceptlon of PPG 150 E I M I Ch IC IPOIHC SCI'IC CO BC emica Ol'p. including two to three propoxy groups considerably im- L (d0) prove the ductllity. Y (d -l TABLE 2 H(OC,H,),,(OC.H,,,).(OC,H,),OH Manufacturer a+c b n y(% by ductility weight (number of bends) Carbowax 6000 Union Carbide Chemicals Co. -470 0 0.02 S 0.10 a Polyox wsn-zus do, l 1000 0 0.10 3 PPG Hodag Chemical Corp. 0 2-3 3 2.5 5i PPG P|02s Dow Chemical Co. 0 l7 3 0.01 3 0.10 3 PPG I200 Hodag Chemical Corp. 0 20-2l 3 0.0! 3 0.|0 3 PPC 2025 Union Carbide Chemicals Co. 0 34-35 3 0.0l 3 0. l0 3 P86 e500 Dow Chemical Co. 0 o 4 0.|0 s 2.5 4 Plumnic LJI Wyandotte Chemicals Corp. 2 l6 3 0.|0 4% Pluronic Lbl do. 4 30 3 0.000] '6 0.00! 5 0.10 4 Pluronic L64 do. 26 3O 3 0.|0 5 Pluronic F68 do. 159 30 3 0.0001 iv,

0.001 s 0.|0 4% Pluronic L81 do. 5 38 3 0. l0 5% Pluronic F88 do. 204 38 3 0. l0 s No addition 5 When R, is a hydrophobic final group, b O and R OH, a molecule is obtained whose solubility in water is determined by the number of ethyleneoxide groups in the hydrophilic tail. Such compounds are typ- For the chemical data regarding these compounds and those of the compounds which will be further men- 65 tioned reference is made to Mc.Cutcheon's Detergents and Emulsifiers 1967 Annual, J. W. Mc. Cutcheon lnc.

R may alternatively be an alkylaryl group such as, for example, an octylphenyl, nonylphenyl or dodecylphenyl group. Relevant compounds are alkylarylethers of polyethylene glycol: C ll Ar (OC H L OH. Active ethoxylated alkylphenols which are commercially available are, for example:

Andros P (series compounds) alkylphenol Chemfi' Arnpilan NP alkylphenol Marchon Products Ltd.

Hyonic PE (series) alkylphenol Nopco Chemical Co.

lgepal CA (series) octylphenol General Aniline 8: Film Corp. CO do. nonylphenol DM do. alkylphenol Lessagene do. alkylphenol Chem-Y Lissapol N( do. nonylphcnoi l.C.l.

Lubrol E alkylphenol l.C.I.

L nonylphenol Neutronyx 600 (series) alkylphenol Onyx Chemical Poly Tergent E (series) nonylphenol Olin Mathieson G do. octylphenol Chemical Corp.

Retzanol NP (series) alkylphenol Retzlofl' Chemical Co.

Renex 600 (series) nonylphenol Atlas Chemical lnd.

Tergitol P (series) dodecylphenol Union Carbide Corp. NPt do. j nonylphenol Triton N do. J nonylphenol Rohm and Haas Co. X do. octylphenol The final hydroxyl group of alkyl and alkylary ethers of polyethylene glycol may be esterified with sulphuric acid. R, then changes into sulphates are produced the alliyl and alkylaryl ethers of polyethyleneglycol, which are anionactive. Suitable sulphates are for example:

Bmpicol BS8 sulphated laurylether of polyethyleneglycol (Na) Marchon Products Ltd. Sipex EA sulphated laurylether of polyethyleneglycol (NI-l Alcolac Chemical Co. Alipal CO-433 alkylphenylether of polyethyleneglycol (Na) General Aniline & Film Corp. C0-436 alkylphenylether of polyethyleneglycol (Nlh) General Aniline & Film Corp. Neutronyx 8-30 alkylphenylether of polyethyleneglycol (Na) Onyx Chemical Co. 8-60 alkylphenylether of polyethyleneglycol (NH Onyx Chemical Co.

The final hydroxyl group of alkylethers and alkylaryl ethers of polyethylene glycol may alternatively be esterified with phosphoric acid. In this case R becomes The relevant phosphate esters are anion-active. Examples are:

Antara LB-400-acid phosphate ester of an alkylether of polyethylene glycol-General Aniline & Film Corp.

Gafac RE-lO-acid phosphate ester General Aniline & Film Corp.

Rozak BD-COC-phosphate ester of the oleylether of polyethylene glyc0lRozilda Laboratories, Inc.

Wascope 9J2 acid phosphate ester of alkylphenylether of polyethylene glycol Wasco Laboratories.

9P1 glycol Wasco Laboratories 9P2 glycol Wasco Laboratories An active compound is also the nonionic Victawet 12 from the firm of Staufi'er Chemical Co., a tertiary phos phate ester defined by the formula:

It is a remarkable that fatty acid esters of polyethylene glycols, for example, compounds of the Myrj-series (Atlas Chemical lnd.) or of the Tween-series (Atlas Chemical Ind.) greatly reduce the deposition rate of copper from copper-plating solutions when the concentration increases generally before reaching a suitable improvement of the ductility. Consequently they are less suitable for use within the scope of the present invention. The activity of a number of these micelleconstituting surface-active compounds of the non-ionic and anionic type will hereinafter be described in detail.

EXAMPLE [ll Two methods of activation of hard paper substrates provided with an adhesive were used: method A: the photochemical production of silver nuclei described in Example I, and; method B: the production of palladium nuclei, Palladium nuclei: Plates (25 sqcm} of chemically roughened hard paper provided with an adhesive (Example I) were activated for the electroless copper deposition by successively treating them at room temperature in a stationary solution of 10 grams of tin (ll) chloride and i0 mls of hydrochloric acid in 1 litre of deionized water (3minutes),

deionized water (1 minute),

a stationary solution of 0.2 gram of palladium (ll) chloride and 10 mls of hydrochloric acid in 1 litre of deionized water (3 minutes) running deioinized water (10 minutes).

The plates were turned about after 30 seconds in the tin (ll) chloride and palladium (ll) chloride solutions. The copper-plating solution used for this Example had the following composition:

0.028 mol copper sulphate (5 8,0),

0.030 mol ethylenediarninetetra-acetate (4 Na),

0.10 mol sodium hydroxide,

0.13 mol formaldehyde,

z percent by weight of polyoxyethylene derivate,

water up to 1 litre.

This solution was used at a temperature of 50C. The polyoxyethylene derivates used and the results obtained are gathered in Table 3.

per deposition by successively treating them at room temperature, while being shaked, in:

a solution of 50 grams of tin (ll) chloride and t mls 7 TABLE 3 lulyoxyethylenenumber '1. acti- Ducderivate Class Manufacturer mol. of (36 by vation tiliweight ethoxy weight method ty groups Surfactant 08-44 alkylphenoxy-P.O.E.- Rohm and Haas Co. approx. appr. 0.l0 B 6 phosphate-ester 800 8 Triton X I00 octylpl'ienylether do. 650 9-]0 0.005 A ft 0.02 A l V: 0.05 A 4 0.10 A 4 Lissapol N nonylphenylether l.C.l. 695 ll 0.05 A 3 Triton X 102 octylphenylether Rohm and Haas Co. 780 IZ-l 3 0.00l B 2% Triton X I65 octylphenyletlier do. 9|0 to 0.005 B 3 Brij 35 Laurylether Atlas Chemical Ind. 930 0.00l A 2 0.02 A 4 0.10 A 7 Triton X 305 octylphenylether Rohm and Haas Co. 1530 0.00l B 3 Triton OS l5 gecthoxyleerd Na'salz do. 2390 0.000l B A 0.0] B 4 0. l A 5 l A 6 Gafac RE 610 phosphate-ester General Aniline 8:. Film 2440 33 0.02 A 4 0.]0 A 5 l A 4 The compound pulp 30. a lauryl ether of polyethylene glycol having :1 mol. weight of approximately 320 and 3-4 ethoxy groups provides copper layers of insufficient ductility.

A further type of compounds is obtained when in the general formula R H, B O,

C,,,H,,,, is a paraffin tail. In that case an ethoxylated secondary amine is concerned when R; H, or an ethoxylated tertiary amine when R,-, is, for example, a polyethoxy group: R, (C- HJJMH. Closely related therewith are ethoxylated fatty acid amides and R is then, for example,

0 iL-Cdiut (compounds of the type Ethomld of Armour Industrial N Chemical Co.)

EXAMPLE IV Glass plates (8 sq.cm) slightly roughened with carborundum powder were activated for the electroless copof hydrochloric acid in 1 litre of deionized water (2 minutes) deionized water (1 minute) a solution of 0.25 grams of palladium (ll) chloride and 10 mls of hydrochloric acid in l litre of deionized water (1 minute) running deionized water (1% minutes) A copper layer 15 20 um thickness was deposited at 50C on the plates thus pretreated. 200 mls of copper-plating solution were used for each plate. This solution had the following composition:

0.028 mol copper sulphate (5 H O),

0.030 mol ethylenediaminetetra-acetate (4 Na) 0.10 mol sodium hydroxyde 0.l2 mol formaldehyde 0.1 percent by weight of an ethoxylated fatty amine deionized water up to 1 litre. The following polyethoxy compounds were used:

a. Sipenol lTl5 fatty amine, l5 ethoxy groups A]- colac Chemical Corp.

b. Sipenol 1Sl5 fatty amine, l5 ethoxy groups Alcolac Chemical Corp.

c. Sipenol lS50 fatty amine, 50 ethoxy groups- Alcolac Chemical Corp.

d. Ethomene C/20 tertiary fatty amine, l0 ethoxy groups Armour Industrial Chemical Co.

e. Ethomene 8/20 tertiary fatty amine, l0 ethoxy groups Armour Industrial Chemical Co.

f. Priminox T-IS secondary fatty amine, l5 ethoxy groups Rohm and Haas Co. (C H C HBO-44) g. Priminox T-25 secondary fatty amine, 25 ethoxy groups Rohm and Haas Co.

The copper layer deposited from a solution without polyethoxy compound had a ductility of one-half bend. The layers deposited from solutions including an addition had the following ductilities:

Addition bends a 2 b 3 c 4% d 2V; e #55 f 3% g 3% Compounds which are interesting within the scope of the present invention are the thioethers of a higher al= kylmercaptane and polyethylene glycol defined by the formula: l"!(()CJL) a -Sc ll (R H; R; an ers; b

it is known that organic sulphur compounds enhance the stablity of electroless copper-plating solutions. However, it is also known that these compounds increase the brittleness of the deposition and that they can generally be used only in a very small concentration because otherwise they suppress the copper deposition completely. When a sulphur atom enhancing the stability and increasing the brittleness and a number of ethoxy groups enhancing the ductility are built in in the W 7 same molecule, such as is the case in the abovementioned ethoxylated thioethers, then it may be expected that the ductility of the deposited copper will be acceptable in the presence of sufficient ethoxy groups while the stability will be enhanced by the presence of the thioether bridge. If necessary the ductilityenhancing effect may be increased by adding a polyalkylene glycol or a surface-active polyethoxy compound of one of the types described so far.

As shown in Example V this consideration may be realized with the surprising effect that the concentration of the thioether was much less critical in connection with the effect on the deposition rate than that of other stabilising organic sulphur compounds.

EXAMPLE V Glass plates which were activated for the electroless copper-plating process as described in the previous Example were coated with a copper layer of l5 20 pm by treating them at 50C in a copper-plating solution of the composition:

0.05 mol copper sulphate (5 H O) 0.075 mol ethylenediaminetetra-acetate (4 Na) 0.30 mol sodium hydroxide 0.12 mol formaldehyde 0.01 percent by weight of Carbowax 4000 0.00l percent by weight of ethoxylated thioether deionized water up to 1 litre.

The following non-ionic ethoxylated thioethcrs were used:

a. Siponic SK thioether of polyethylene glycol Alcolac Chemical Corp.

b. Sterox SE thioether of polyethylene glycol Monsanto Co.

c. Nonic 260 tertiary dodecyl thioether of polyethylene glycol Pennsalt Chemicals Corp. (5,7 ethoxy groups).

The ductility of the copper layer which was deposited from a solution without polyethoxy compound was one-half bend. The ductility of the copper layers deposited from solutions including additions was at least three bends. The durability of a bath including additions was a factor of 3 to 4 better than that of a bath without an addition. Solubility permitting the concentration of the thioether may be increased to 0.1 percent by weight before the copper deposition is unacceptably delayed.

As already previously noted, a number of bivalent sulphur compounds added in a quantity which is smaller than that which completely prevents the copper deposition has a stabilising effect on an electroless copper-plating solution so that it is durable for a longer period. U.S. Pat. No. 3361580 describes the action of a few stabilisers (thiourea, potassium polysulphide, thioglycol acid and Z-mercaptobenzothiazole) which are used in quantities of 0.001 to 0.1 milligrams per litre of solution, although the magnitude of the technical effect is not clearly mentioned. When tracing the described examples, the stabilising effect is unmistakably present, but in so far as they can be deposited to the required thickness the copper layers have a completely insufficient ductility. An experiment on the stabilising effect of Z-mercaptobenzothiazole is described in Electronic Industries of Sept. 1962, pages 1 17 e 119.

In the experiment performed in connection with the present invention it was attempted to enhance the stalyalkoxy compound in a concentration ensuring the deposition of satisfactorily ductile copper by addition of one of the known bivalent sulphur compounds. it was found that it is very difficult to enhance the stability of these baths to an optimum extent while maintaining an acceptable ductility of the deposited copper. A number of examined compounds showed that l-phenyl-S- mercaptotetrazole in combination with polyalkoxy compounds, which had not been previously described as a stabiliser for electroless copper-plating solutions, led to the envisaged object. The quantity of l-phenyl-S- mercaptotetrazole which is added is to be between fi iiji a nd l milligram per litre of solution (including the limit values). The following Example illustrates this embodiment of the copper-plating bath according to the invention.

EXAMPLE VI Plates of chemically roughened hard paper provided with an adhesive (25 sq.cm) were subjected to the formation of palladium nuclei in the manner as described with reference to Example Ill in order to activate these plates for electroless copper-plating. The plates were copper-plated at 50C while being stationary in 200 mls of the following solution:

0.05 mol copper sulphate (5 H O) 0.075 mol ethylenediaminetetra-acetate (4 Na) 0.30 mol sodium hydroxide 0.l9 mol formaldehyde 0.5 mg l-phenyl-5-mercaptotetrazole l g Carbowax i540 deionized water up to 1 litre.

A copper layer of 20 nm was deposited within 5 hours and had a ductility of at least three bends. When the polyalkosy compound was omitted a brittle copper layer was deposited bend). The durability of the bath was enhanced by a factor of 8 due to the addition of l-phenyl-S-mercaptotetrazole. Similar results are obtained when instead of l g of Carbowax 1540, 2 grams of Triton QS-l5 are added.

The choice of the water-soluble copper salt for electroless copperplating solutions is mainly determined by economic considerations. Copper sulphate is preferred, but the nitrate, halogenides, acetates and other soluble salts of copper may alternatively be used.

In the electroless copper-plating solutions cupric ions and complexing agent as a rule constitute complexes at a molecular ratio of l l, but generally an excess of complexing agent will preferably be used. There are many known complexing agents for cupric ions. Preferably the invention employs Rochelle salt (potassiumsodium tartrate), triethanolamine and alkali salts of N- hydroxyethylethylenediaminetriacetic acid, ethylenediaminetetra-acetic acid and diethylenetriaminepentacetic acid and mixtures thereof.

Reducing agents which are used in alkaline electroless copper-plating solutions are formaldehyde and compounds or derivates producing formaldehyde such as paraformaldehyde, glyoxale and trioxane.

Among the alkalihydroxydes, sodium hydroxyde is preferably used for reasons of economy. The baths may contain less essential constituents such as, for example, buffers and sodium carbonate.

As regards the operating temperature of the baths, the fact should be taken into account that the rate by which copper is deposited increases as the temperature stability of the solutions, whereas baths containing strong complexing agents will be used preferably at comparatively high temperatures, in some cases even up to 90C. Thus, solutions in which potassium-sodium tartrate, triethanolamine and/or N-hydroxyethylethylenediaminetriacetate (3Na) are used as complexing agents may be used at temperatures of 15C to C; solutions based on ethylenediaminetetraacetate (4 Na) may be used at temperatures of 20C to 80C and solutions based on diethylenetriaminepentaacetate (5 Na) may be used at temperatures of C to 90C. The last-mentioned baths have the advantage that they do not deposit at room temperature and are then very stable. When not in use, these baths are therefore preferably allowed to cool down to room temperature. The following examples illustrate the invention when using the different complexing agents in a temperature range of from l5 to 90C.

EXAMPLE Vll Similar activated substrates as those used in Example V] were electroless copper-plated with a layer of 15 20 p.111 thickness.

Bath compositions and results CuSO (5l-l,O) KNA tartrate HEDTA NaOH HCHO Na,CO, Surfactant Carbowax R Bends 0.02Bmol/l 0.15 mol/l 0.40mol/l 0.32mol/l 0.l0molll 0.7 run/h A 0.028 0.15 0.40 0.32 010 l0gfl 0.3 4 0.023 0J5 0.40 0.32 0.10 ZUg/l 0.2 3 0.02 0.80 0.20 0.32 0.80 not A determined (HEDTA (3Na) is the trisodium salt of N hydroxyethylethylenediarnetriaeetate) At 20C a deposition rate of 0.7 um/hour is hypercritical, but a rate of 0.45 [.Lm/hOUl' is almost critical.

EXAMPLE Vlll Using the same kind of activated substrates the following results were obtained with the copper-plating solution mentioned in the table while using a bath temper ature of 35C (see tables page C0504 KNa (511,0), tartrate, Rate, mDl/l. mol/l pTXL/ll. Bends 0.014 O. 033 l) l: 0. 014 0. 033 l. 1 5 0.014 0. 033 l. 3 3 0. 014 0. 033 0v 7 3 0. 014 s c s s 1.0 3 0. 014 l. 0 2

I Not determined.

NOTE.TEA is triethanolamiue.

' C b ax Rat EDIA, NaOH, ncuo, ow j CuSOAEIhO), mol/l. mol/l mol/l moi/l. g/l. cmJ/hour Bends 0.10 0.15 0.13 0. 02 2 0. l0 0. 15 0.13 0.1 l 2 0.10 0.15 0.13 1.0 (1.4 4 0.10 0.15 0.13 l0 0. 2 [i can still be used is determined to a great extent by the EXAMpLE x nature of the complexing agent for the cupric ions. Baths containing weak complexing agents must be used at a comparatively low temperature with a view to the Copper layers of approximately 20 pm thickness were deposited on glass plates which were activated for the electroless copper deposition in the manner as described with reference to Exarnpie IV by treating these plates for 4 hours (deposition rate 5 urn/hour) with the below-mentioned copper-plating solution which was maintained at 35C and which was not stirred. Compo- 5 sition of copper-plating solution:

0.028 mol copper sulphate (5 H20) 0.065 mol triethanolamine 0.20 mol sodium hydroxide 0.19 mol formaldehyde [0 l0 g Carbowax 4000 (deionized water up to 1 litre).

The deposited copper layers could stand three full bends. A similar bath without Carbowax 4000 yielded pm of copper deposition per hour, but the ductility was then l bend.

EXAMPLE X Glass plates (8 sq.cm) were superficially roughened for 1% minutes with carborundum powder (particle dichloride and 10 mls of hydrochloric acid in 1 litre of deionized water (2 minutes at 22C).

deionized rinsing water in minutes) a solution of 0.25 grams of palladium (ll) chloride and 10 mls of hydrochloric acid in l litre of deionized water (2 minute at 22C).

deionized rinsing water (2 minutes) The copper deposition rate was varied by means of the concentration of the copper salt in the copper plating solution. The composition thereof was as follows:

J: mol copper sulphate (5 H,())

0.20 mol ethylenediaminetetraacetate (4 Na} 0.l0 moi sodium hydroxyde O.l8 moi formaldehyde 1 g Carbowax 4000 deionized water up to 1 litre. 200 mls of copper-plating solution were used for each plate. The operating temperatures of the baths were 50C, 60C and 75C.

EXAMPLE XI The copper deposition from a bath of the composition below was compared using three kinds of activated substrates:

a. chemically roughened hard-paper substrates provided with an adhesive (Example I), photochemically activated for the copper deposition in the manner described in Example I (formation of silver nuclei);

b. the same hard paper substrates activated in the manner described in Example X (formation of palladium nuclei);

c. mechanically roughened glass substrates (Example X) activated in the manner described in Example X (formation of palladium nuclei). Composition of the copper-plating solution:

0.028 mol copper sulphate (5 11,0)

0.030 mol ethylenediaminetetraacetate (4 Na) 0.20 mol sodium hydroxyde 0.12 mol formaldehyde l g Carhowax 4000 deionized water up to 1 litre.

Layers of approximately 20 pm thickness were again deposited. The results may be summarized as follows:

No significant differences could be found in the deposition on the different substrates. However, the tendency of a better ductility at a higher temperature of the bath becomes clearly manifest.

EXAMPLE Xll Copper was deposited for 4 hours on glass pistes The following results were obtained.

Thickness of Average deposition Number Bath temp. x the deposited rate of C molll copper layer (um/hour) bends 0.03 24 1.4 4 0.05 20 3.3 4 0.06 20 S 3 0.07 23 i0 is 0.03 20 2.8 5 005 I8 4 6 0.07 20 9 H6 2 75 0.03 2i 6 8 0.05 31 l3 5 0.07 21 2| 2 These baths showed signs at spontaneous decomposition at the end of the period it is clearly apparent that the critical rate at which copper having a ductility of at least two bends is deposscribed in Example X from a copper-plating solution of ited increases as the bath temperature increases.

which were roughened and activated in the manner dethe composition:

0.028 mol copper sulphate (5 Hp) 0.04 mol diethylenetriaminepentaacctate (5 Na) J0 mol sodium hydroxyde 0.l9 mol formaldehyde grams surfactant 0844 deionized water up to I litre. i

The layers which had a thickness of approximately um could stand 4 bends. After deposition the bath was cooled down to room temperature and it was brought to 70C again after 24 hours whereafter glass plates were copper-plated again.

Without the addition of surfactant QS-44 dark copper was deposited which could only stand 1% bends.

What is claimed is:

1. An alkaline aqueous electroless copper-plating bath for depositive ductile copper, which bath is free of inorganic cyanides, organic nitriles and compounds of La, the rare earths Mo, Nb, W, Re, V, As, Sb, Bi and Ac, said bath having a pH of about lll3.5 and containing per liter of water 0.0] l.l0 mols of a watersoluble copper salt, 0.01-0.35 mols of formaldehyde or a formaldehyde producing compound, 0.01 0.80 mols of at least one coupling compound capable of forming a soluble complex with cupric ions in an alkaline solution, 0.05 0.50 mols of an alkali metal hydroxide and a water soluble polyalkylene oxide compound containing at least four alkylene oxide groups of two to four carbons per molecule in an amount sufficient to cause the resultant copper layer to be ductile.

2. The copper-plating bath of claim I wherein the polyalkylene oxide compound is defined by the formula:

R, (C H.O),, (C,,H ,,O),, (C H. 0), R in which formula 0 h c 4, n 0-4, R being H and R being OH when n is 0, 3 or 4, R being alkyl or alkaryl and R, being OH, esterified or unesterified hydroxy, sulfate or bath temperature: C

phosphate groups when n 0 and when n 6, R is H and R, is fatty acid amino, fatty acid amino or an alkyl substituted mercapto.

3. The copper-plating bath of claim 2 wherein the polyalkylene oxide compound is a polyalkylene glycol containing at least 4 ethoxy or propoxy groups.

4. The copper-plating bath of claim 2 wherein the polyalkylene oxide compound is an ethoxylated fatty acid amine or an ethoxylated fatty acid amide.

5. The copper-plating bath of claim 2 wherein the polyalkylene oxide compound is an ethoxylated thioether containing an alkyl group.

6. The copper-plating bath of claim 1, wherein in addition 0.01-l mg per liter of l-phenyl-S-mercaptotetrazole is present as a stabilizer.

7. The copper-plating bath of claim 1 wherein the complexing agent for cupric ions is selected from the group consisting of potassium-sodium tartrate, triethanolamine and N-hydroxyethylethylene diaminetrisodiumacetate and the temperature of the bath is between 15 and 40C.

8. The copper-plating bath of claim 1 wherein the complexing agent for cupric ions is ethylenediaminetetrasodium-acetate, and the temperature of the bath is between 20 and C.

9. The copper-plating bath of claim 1 wherein the complexing agent for cupric ions is diethylenetriaminepenta-sodiumacetate, and the temperature of the bath is between 60 and C.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,804,638 DATED April 16, 1974 !NVENIOR(S) 1 HENDRIK JONKER ET AL It as certified that em): appears in the above-identified patem and ihat said Letters Patent are hefeby cemented as shown below:

Col. 19, line 21, "1.10" shoud be 0.10

Signed and Sealed this Thirty-first D3) of August 1976 {SEAL} RUTH C. MASON C. MARSHALL DANN Am'mng ()jjuer ('ummisximmr m Iun'ms uml Tradvmurks

Claims (8)

1. 2. The copper-plating bath of claim 1 wherein the polyalkylene oxide compound is defined by the formula: R1 (C2H4O)a (CnH2nO)b (C2 H4 O)c R2 in which formula a + b + c > or = 4, n 0-4, R1 being H and R2 being OH when n is 0, 3 or 4, R1 being alkyl or alkaryl and R2 being OH, esterified or unesterified hydroxy, sulfate or phosphate groups when n 0 and when n 6, R1 is H and R2 is fatty acid amino, fatty acid amino or an alkyl substituted mercapto.
2. 3. The copper-plating bath of claim 2 wherein the polyalkylene oxide compound is a polyalkylene glycol containing at least 4 ethoxy or propoxy groups.
3. 4. The copper-plating bath of claim 2 wherein the polyalkylene oxide compound is an ethoxylated fatty acid amine or an ethoxylated fatty acid amide.
4. 5. The copper-plating bath of claim 2 wherein the polyalkylene oxide compound is an ethoxylated thioether containing an alkyl group.
5. 6. The copper-plating bath of claim 1, wherein in addition 0.01-1 mg per liter of 1-phenyl-5-mercapto-tetrazole is present as a stabilizer.
6. 7. The copper-plating bath of claim 1 wherein the complexing agent for cupric ions is selected from the group consisting of potassium-sodium tartrate, triethanolamine and N-hydroxyethylethylene diamine-trisodiumacetate and the temperature of the bath is between 15* and 40*C.
7. 8. The copper-plating bath of claim 1 wherein the complexing agent for cupric ions is ethylenediamine-tetrasodium-acetate, and the temperature of the bath is between 20* and 80*C.
8. 9. The copper-plating bath of claim 1 wherein the complexing agent for cupric ions is diethylenetriamin-epenta-sodiumacetate, and the temperature of the bath is between 60* and 90*C.

Images