DK141411B - Bath for depositing metal coatings without external power supply. - Google Patents

Description

(11) PUBLICATION 141411 DENMARK («> in * .ci.'c 23 c 3/02 f (21) Application No. 559/67 (22) Filed on 51 Jan 1 $ 67 (23) Running day 51 Jan. 19 ^ 7 (44) The application presented and 1 r ΡΛ

the petition published on 10 March. 15 OU

DIRECTORATE OF.

THE PATENT AND TRADEMARKET SYSTEM (30)

Feb 1 1966, 525865, US

Feb 1 1966, 5259Ο2, US

(? 0 PHOTOCIRCUITS CORPORATION, Glen Cove, New York, US.

(72) Inventor: Frederick William Schneble Jr., 16 Karen Court, Oyster Bay, Long Island, NY, US: John "McCormack, 116 Milburn Lane, Roslyn Heights, New York, US: Rudolph John Zeblisky, 4l Glenwood Drive, Haup = peacock, New York, US.

(74) Plenipotentiary in the proceedings:

Dansk Patent Kontor ApS. ______ (54) Bath for depositing met alover features without external straw supply.

The present invention relates to a bath for depositing metal coatings without external power supply on catalytically active or activated surfaces or surface areas, which bath contains at least ions of the metal to be deposited, a complexing agent and a reducing agent therefor, and a component for adjusting pH value of a desired size.

Baths of this kind are known e.g. from Danish Patents Nos. 105-901 and Nos. 131,998.

Such baths are particularly suitable for metallizing insulating surfaces on articles which have been appropriately treated to make them susceptible to uptake of electrically deposited metal.

2 141411

Most powerless metal deposition baths of the aforementioned kind produce metal deposits containing a substantial amount of hydrogen for reasons which will be explained in more detail below. Such deposits are brittle, break by vibration and bending and otherwise have poor ductility. For this reason, such baths are generally unsatisfactory for use where robust, adherent metal deposits that can withstand rough mechanical treatment and bending forces are desirable and the tendency of these powerless metal deposits to provide brittle metal deposits has delayed the use of such baths for use. .g. manufacture of printed circuits and metallization of plastics in general.

The precise mechanism by which baths of the aforementioned type are made of metal-free deposition, e.g. however, the following theory is sought to provide a rational explanation of this phenomenon.

In powerless copper deposition from a bath containing a solvent, a source of cup rions, a reducing agent for cup rions, a complexing agent for cup rions, and a pH regulator, the reducing agent is oxidized at sensitized deposition surface areas and releases electrons to such regions. Cup rions in contact with such regions collect the free electrons and reduce to copper atoms deposited on the adjacent surface areas and aggregate to form a copper metal deposit.

The potential at which the process takes place is a compromise, or mixed potential, between the two potentials which characterize the oxidation of the reducing agent and the reduction of the cuprians.

To illustrate the mechanism, for example, a particularly useful powerless copper deposition bath may be taken in which the reducing agent is formaldehyde and the source of cup rions is a copper salt such as copper sulfate.

Using the mixed-potential theory described above, it must be said that the formaldehyde is oxidized to hydrogen and formations at the sensitized surface at which deposition takes place and an electron is emitted to the surface for each molecule of oxidized formaldehyde. The released electrons are absorbed on their side by the cuprous ions at or in contact with the surface, causing local deposition of copper.

However, it is known that all the constituents of a bath of the kind in question affect the bathing ability of the bath and that the bath is constantly changed during consumption of the bath's components.

According to Danish Patent No. 131,998, such baths can be improved by adding small amounts of compounds of e.g. the metals vanadium, arsenic and antimony, with such additives it is possible to keep baths in dynamic equilibrium for a long time without adversely affecting the bathing rate of deposition or the physical properties of the coatings obtained.

The surface on which the metal deposit takes place can be considered as a charged interface with structure as an electric bilayer.

For a description of the structure of the electrical bilayer at such a charged interface, reference is made to Proc. EOY.

Soc., Series A, ig63, pp. 55-79, and Bockris, Modem Aspects of KLectro-chemistry ΪΓο. 1, 154, pp. 103-173 ·

What happens during metal deposition from simple composite baths of the present invention appears to be that hydrogen is adsorbed on both the inner and outer layers of the electric bilayer, released from the reducing agent. This causes the deposited metal layer to become porous and thus get some brittleness.

The bath known from Danish Patent No. 131,998 is distinguished not only by good stability but also by providing deposits with excellent ductility. This can be explained from the double-layer theory by the fact that the said additives in the ionized form are very easily moving and migrate to the inner layer and are adsorbed there, thus reducing the otherwise occurring hydrogen adsorption.

It has now been found that an improved ductility can also be obtained in other ways.

This is achieved when the bath according to the invention, according to the invention, further contains phosphorus in an amount of between 0.02 and 0.1 mole per day. liter.

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The explanation for this is that this addition is adsorbed electrostatically or by coulombic forces to the outer layer of the bilayer, which prevents hydrogen adsorption and simultaneously inhibits hydrogen adsorption on the inner layer.

The necessary phosphorus can be added e.g. as organic or inorganic phosphorus-containing salts, acids and bases. Phosphate, tetra-pyro-phosphate and hexametaphosphate salts of alkali metals, alkaline earth metals and ammonium are preferred for this use. Preferred for use are sodium, potassium and ammonium phosphates and polyphosphates.

The aforementioned compounds are merely examples of those capable of providing phosphorus-containing ions suitable for the present use.

Here, it should be noted that the electrostatically adsorbable ions described are present in readily detectable amounts, thereby facilitating operation control.

The electrostatically adsorbable ions described are maintained as mentioned in the streamless metal deposition bath at a concentration of 0.02 to 0.1 mole phosphorus per 1 solution, preferably, however, between 0.03 and 0.08 moles per ml. First

However, it should be noted that the amount of electrostatically adsorbable ions will vary with the nature and activity of the ion used and with the composition of the solution and the conditions, e.g. temperature, concentration and pH below which it is used.

The upper limit of such ions is an amount that will prevent the electroless deposition of metal under the conditions of use. The lower limit is the middle amount of ion, which will be effective in providing the results of the present invention, again under the special conditions of use.

When using baths for powerless metal deposition, it is well known that the baths are used up during their use and that their constituents must be supplemented from time to time, including maintaining their desired pH.

5 14U11

This also applies to the phosphorus content of the hate in question, which is regulated to the optimum value for the hate composition used.

To obtain the hottest results, surfactants in an amount of less than 5 δ per 1 is added to the hate. Examples of suitable surfactants are organic phosphate esters and oxyethylated sodium salts.

The baths can be used at widely varying temperatures, e.g. between 15 and 100 ° C, but they will usually be used between 20 and 80 ° C. As the temperature increases, it is usual to see that the coating rate is increased, but the temperature is not very critical and within the usual operating range excellent shiny, ductile deposits of powerless deposited copper are obtained with: reduced hydrogen content.

Performance data for baths of the present invention are given in Table I.

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The solutions mentioned in Table I contained approx. 1 ml / l of an organic surfactant.

As can be seen in Table I, the presence of the phosphorus ductility of the copper coating improves to a truly remarkable degree.

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The use of the phosphorus compounds described also greatly improved the stability of the powerless copper deposition solution.

When metal is to be coated using powerless copper deposition solutions, the surface to be coated must be free of grease and other contaminants.

When a non-metallic surface is to be coated, the surface area to receive the coating must first be sensitized to make it catalytic to the uptake of electroless deposited copper, as explained above.

When metal surfaces are to be coated, they should be degreased and then treated with an acid, such as hydrochloric or phosphoric acid, to release them from oxides.

After pretreatment or sensitization, the surface to be coated in the autocatalytic metal baths is immersed and allowed to remain there until a metal coating of the desired thickness has been built up.

As noted above, the solutions described herein are advantageous for use in the production of printed circuits. Eg. For example, parts of the surface of an insulating support in the form of a desired circuit pattern may be sensitized to receive powerless deposited metal. After sensitization, the support is immersed in the solution of the type described and allowed to remain there until a metal coating of the desired thickness has been built up. The circuit may be formed on one or more surfaces of the carrier. If desired, connections may be provided between the surfaces by drilling or closing holes and sensitizing these side walls prior to immersing the support in the powerless metal deposition solution. In this embodiment, metal is deposited on the circuit pattern as well as on the 14UT1 8 walls surrounding the holes to form connections.

In order to improve the stability of the metal deposition solutions described herein, certain sulfur-containing compounds can be maintained therein during operation.

Among the organic sulfur compounds are the following: aliphatic sulfur-nitrogen compounds such as thiocarbamates, e.g. thiourea; 5-membered heterocyclic compounds containing S-ΪΓ in the 5-membered ring such as thiazoles and isothiazoles, e.g. 2-mercapto-benzene-thiazole; dithiols, e.g. 1,2-ethandi-thiol; 6-membered heterocyclic compounds containing S-3ST in the ring such as thiazines, e.g. 1,2-benzisothiazine, benzothiazine, thioamino acids such as methionine, cystine and cysteine; thio derivatives of alkyl glycols such as 2,2'-thiodiethanol, dithiodiglycol and thioglycolic acid. Among the inorganic sulfur compounds are: alkali metal sulfides, e.g. sodium sulphide, potassium sulphide, sodium polysulphide, alkali metal thiocyanates such as sodium and potassium thiocyanates and alkali metal dithionates such as sodium and potassium diionate.

The above-mentioned sulfur compounds are just examples of sulfur compounds capable of stabilizing autocatalytic copper deposition baths.

The amount of sulfur compounds required is a small effective amount and will vary depending on the individual compound used, from traces to approx. 300 parts per million (ppm) or more.

For most sulfur compounds, 1 ppm will be the upper limit and approx. 0.001 ppm the lower limit. A good working range for most sulfur compounds is between 0.01 and 0.2 ppm.

Solutions containing a small effective amount of sulfur component are particularly useful in the preparation of printed circuits. In the absence of sulfur, there is a tendency for powerless coating solutions of the type described in non-sensitizing areas of the insulating carriers after prolonged immersion in the solutions to become sensitized and to be spot-coated with metal. It will be appreciated that powerless deposition of metal in the area of the support where metal is not desired would create difficulties with the control technique in producing printed circuits.

Claims (2)

9 141411 In addition, when commercially catalytic metal deposition baths are used commercially, there is a tendency for undesirable metal deposition on insulating walls of "containers that hold the electroless metal deposition solution over a longer period of time. metallic surfaces on the areas that have been sensitized to form catalytically active points, these baths have a remarkable ability to distinguish non-sensitized nonmetallic areas from those that have become, and to only Although a non-pretreated non-metallic surface, including the walls of the tubs containing the baths, is exposed to the baths for a prolonged period of time, the tendency to form scattered stain deposits of metal is substantially reduced. , if it is not completely eliminated. It should be noted here that the above mentioned undesirable copper deposits g preferably occurs in such baths which are substantially free of iron ions. Baths containing phosphorus according to the invention are particularly useful, provided they do not contain iron ions. However, it has been found that adding complex cyano-metal compounds, such as ferricyanides or ferrocyanides to powerless copper deposition solutions of the type described herein, results in an increase in deposition rate. Accordingly, the present invention relates to the addition to or maintenance in the solutions of small effective amounts of hexacyanoferrate (II) and hexacyanoferrate (III). Generally, the amount of such salts is from 1 to 320 parts per liter. million, calculated as iron (Fe). 1. Bath for depositing metal coatings without external power supply on catalytically active or activated surfaces or surface areas, which bath contains at least ions of the metal to be deposited, a complexing agent and a reducing agent thereof, and a component for adjusting