Method of producing conductor layers on dielectric surfaces

BACKGROUND OF THE INVENTION

1. Field of the Invention.

0001The present invention pertains to modification of qualities of a dielectric surface, in particular to render a dielectric surface to be an electric conductor. The invention may be used e.g. in various areas of industry for the preparation of dielectric surfaces of electroplating, especially for nickel-plating. Dielectric items which are metal-coated by processes of the invention may be used e.g. where a decorative or protective function is required, in manufacturing press-forms using the galvanoplastic method, or for assemblies for shielding electromagnetic emission.

2. Background.

0002One existing certain method of producing conductor surfaces is known (USSR patent No 980858, B 05 D 5/12 1982), in which the dielectric surface is treated by amine-salt solution of copper, then immersed in water, then in sulphide solution and then rinsed with water.

0003Using this method, a quality conductor surface can be obtained by repeating the operation sequence described in the USSR patent at least three times. This increases the duration of the entire process, increases the consumption of water and chemicals and makes the use of automated production lines more difficult.

0004In addition, another certain existing process for producing conductor surfaces of cupric sulphide is known (USSR patent No 1762454, H 05 K 3/42, 3/18, 1991), in which dielectric items are immersed into solution of univalent cupric salt, then into a solution of 0.0025 / 0.025 of potassium persulphate, iodine or potassium nitrite solution, then rinsed with water and immersed into sulphide solution of an alkaline metal. This process is carried out at room temperature and each operation is repeated twice.

0005The shortcomings of the method described in USSR patent No 1762454 are the same as the shortcomings described in the preceding patent. In addition, through application of both existing methods, it is impossible to leave an isolated part of the item uncovered, i.e., it is impossible to achieve selective conductor coating.

0006See also the patent application of the Republic of Lithuania No 98-161, published in the official bulletin of Lithuanian State Patent Bureau (VPB) No 5 in 2000. That reported method also has notable shortcomiongs, including problematic use of a cobalt solution.

0007It would be desirable to have new methods to render a dielectric surface electrically conductive.

SUMMARY OF THE INVENTION

0008The present invention enables selective production of quality conductor metal sulphide coatings on a dielectric surface without the use of ammonia hydroxide or amine, and to make the process shorter.

0009The invention also enables producing conductor coatings with the use of stable ionic solutions.

0010More particularly, methods of the invention include treating a dielectric surface with a composition comprising bismuth and with sulfur (sulfide) treatment. Preferably, the dielectric substrate is treated with a solution that contains bismuth ions, particularly trivalent bismuth ions. The treated substrate is then preferably treated with a sulfide solution. A water rinse can be suitably employed between the treatment with bismuth composition and the sulfur treatment.

0011Prior to the treatment with a bismuth composition, a dielectric substrate is suitably etched. A variety of etchants may be employed. Generally preferred is an acidic aqueous solution that comprises e.g. KIO₄, or K₂S₂O₈ and CrO₃.

0012A variety of sulfur compositions also may be employed. An aqueous solution containing a sulfur salt is generally preferred, e.g. a sodium or potassium sulphide water solution.

0013Methods of the invention enable selective production of quality metal sulphide conductor coating on dielectric surface without using ammonia hydroxide, amines or other compounds that form strong complex compounds with heavy metals. In addition, methods of the invention produce conductor coatings uses metal ion solution which are highly stable. That is, in distinction from prior systems, bismuth treatment compositions of the invention are highly stable for extended periods. See, for instance, the results set forth in Table 1 below.

0014The invention also includes articles having a metal plate thereon produced in accordance with the disclosed methods.

0015Methods and articles of the invention are useful for a wide variety of applications, including for forming electrical circuits and conductors such as present on a printed circuit board or other electronic packaging substrate, a metal finish, and other applications such as producing electromagnetic shielding. The methods of the invention are particularly useful to deposit a decorative or protective nickel plate, or other decorative or protective metal layer.

0016Other aspects of the invention arc disclosed infra.

DETAILED DESCRIPTION OF THE INVENTION

0017The invention provides new methods for plating dielectric substrates, particularly polymer substrates such as e.g. ABS (acrylonitrile butadiene styrene) copolymer substrates, epoxy resin substrates, polyetherimide substrates, and the like.

0018The methods of the invention generally include use of a bismuth treatment step. Subsequent treatment with a sulfide material or composition enables quality metallization of the substrate, e.g. with an electrolytic nickel, copper, gold, silver, platinum or other metal plating composition solution. In contrast to other prior systems, plating catalysts such as Pd, or Pd./tin, platinum or other metal need not be employed to deposit the metal layer. Also, unstable treatment solutions such cobalt need not be employed.

0019To enhance the metal deposits on the dielectric substrate, preferably the dielectric substrate is first treated with an ctchant solution that can provide a chemically and physically modified surface that is optimized for subsequent conditioning and plating. Such materials typically contain a strong oxidant and include the acidic compositions discussed above as well as alkali permanganate compositions.

0020Treatment compositions employed in accordance with the invention may be applied to a dielectric substrate by a variety of methods, including by spray application as well as immersion. A treatment composition is typically applied as a solution to a substrate.

0021A variety of bismuth compositions may be employed in accordance with the invention. A trivalent bismuth species is particularly preferred. Both inorganic and organic bismuth materials are suitably employed such as Bi(NO₃)₃, BiCl₂ or Bi(CH₃COO)₃. Those bismuth compositions are preferably present in an acidic aqueous solution, such as a HCI, HNO₃ or acetic acid solution. The solution may contain relatively small amount of the bismuth material, e.g. the solution may suitably be from 0.0001 to about 1 molar in bismuth ions, preferably a bismuth ion concentration of about 0,005 to about 0.5 molar, even more preferably a bismuth ion concentration of about 0.005 to about 0.3 molar in an aqueous treatment solution.

0022The bismuth composition may be applied to a dielectric substrate at room temperature to achieve good results, although the bismuth solution also may be at an elevated temperature.

0023After treatment with the bismuth composition, the substrate is then treated with a sulfur composition, preferably an aqueous solution that contains a sulfide species, e.g. a sulfur salt such as Na₂S or K₂S, or an organic sulfide, such as an alkyl sulfide. N₂S or K₂S is generally preferred.

0024The sulfide composition also may be applied to a dielectric substrate at room temperature to achieve good results, although a sulfide composition solution also may be at an elevated temperature.

0025Times of treatment of a dielectric substrate with the above compositions can vary rather widely. In general, treatment times of from 0.25 to 10 minutes arc suitable, more typically from 0.5 to about 1, 2, 3, 4 or 5 or more minutes.

0026Preferably, a treated dielectric substrate is rinsed with water between treatment steps, i.e. after etching, after bismuth treatment and then after sulfur treatment. The substrate may be suitably dried before plating.

0027A variety of metals may be plated onto a dielectric substrate. Plating compositions are commercially available. For instance, suitable electrolytic copper, nickel and gold plating compositions are available from the Shipley Company (Marlborough, Massachusetts). A preferred nickel electroplating plating composition and method for use thereof is set forth in the examples below. See also, Coombs, <i>Printed Circuits Handbook</i>, (3^rd Edition, McGraw Hill), incorporated herein by reference, for additional suitable plating compositions and uses thereof.

0028Preferred electrolytic copper plating compositions for use in accordance with the invention include an aqueous composition that contains an aqueous solution of CuSO₄ 5H₂O at a concentration of 60 g/l; H₂SO₄ at a concentration of 225 g/l; and Cl ions at a concentration of 50 ppm. The treated substrate to be plated is suitably immersed in an n air-agitated plating tank outfitted with multiple cathode rails and one rectifier and charged with such a copper plating solution. During plating, the following deposition conditions are suitably employed; current density of 14.5 mA/cm²; DC waveform was DC; and plating bath temperature of 25°C.

0029References herein to solutions of materials are inclusive of fluid materials where all solid components are dissolved therein, as well as fluid compositions where one or more added components arc dispersed or otherwise not fully dissolved in the fluid. Preferably, most or all added components arc fully dissolved in the fluid carrier (typically water).

0030The following non-limiting examples are illustrative of the invention. All documents mentioned herein are incorporated herein by reference.

GENERAL COMMENTS TO EXAMPLES

0031In the following examples, products made of dielectric-plates made of ABS (a copolymer of vinyl cyanide, divinyl and styrene) plastic substance arc etched for 5 minutes at room temperature in solution which contains 13M H₃PO₄ and 0.5M K₂S₂O₈ or etched for 5 minutes in 60 °C temperature solution which contains 3.8M H₂SO₄ and 3.8M and CrO₃ and rinsed with water.

0032In the following examples, products of dielectric-shock-resistant polystyrene (SAPS) are etched for 5 minutes in solution containing 17M H₂SO₄ and 0.5M KJO₄ under room temperature and rinsed with water.

0033After etching, the products are treated for 2 minutes in solution which contains 0.005 / 0.300 M Bi(NO₃)₃ or BiCl₃ or Bi(CH₃COO)₃ and 0.01 / 0.35 M HNO₃ or HCl or CH₃COOH, under room temperature. After this, products arc rinsed with water and for further 30 seconds treated in solution containing 0,01 / 0,25 M Na₂S or K₂S at room temperature.

0034When the process is completed, the items are rinsed with distilled water, dried and nickel plated for 15 minutes in Watts electrolyte which contains 1 / 1.2M NiSO₄; 0.15/0.2 M NiCl₂ and 0.4 / 0.5 M H₃BO₃, initial flow density 0,3 A/dm₃, which, along the progress of nickel coating from the point of contact, increases to 3 A/dm₃, under electrolyte temperature of 40° C.

0035Stability of the metal ion solution is assessed, examining the presence of sediment in solution (which means that the solution is unstable) or their absence (which means that the solution is stable).

0036The smoothness of the conductive sulphide coating is assessed visually immediately after the treatment, in daylight, using two parameters: smooth, not smooth.

0037Electrical conductivity of the coating is assessed by the chemical nickel-plating expansion speed from the point of contact, in centimetres per minute.

0038The possibility of selectively producing conductor coating on a dielectric item is assessed by examining whether isolated part of the item is covered in nickel or not.

0039In the following Examples 1 through 7, Examples 1, 3 and 6 arc for control purposes, while Examples 2, 4, 5 and 7 have been prepared in accordance with the proposed method, under different concentrations of bismuth component ions, and using different technological means.

0040In Examples 3, 4, 5, 6 and 7, subjected to treatment are ABS plastic plates with surface area of 50 cm², while in Example 2 there are profiled items made of shock-resistant polystyrene (SAPS) with surface area of 70 cm².

EXAMPLE 1

0041Profiled articles from shock-resistant polystyrene, with surface area of 70 cm², etching 5 minutes at room temperature with 17M H₂SO₄ and 0.5M KJO₄.

0042Items are rinsed with water after etching and treated for 10 minutes in solution which contains 0.01M CoF₃ and 0.35M NH₄OH, under room temperature. After this, the items are rinsed in acetic acid up to pH 5 in acid water and treated for 30 seconds in sulphide solution which contains 0.1 M Na₂S.

0043After treatment, the items are rinsed with distilled water, dried and nickel-plated for 15 minutes in Watts electrolyte, containing (M): NiSO₄ - 1.2; NiCl₂ - 0.2 and H₃BO₃ - 0.5; initial flow density 0.3 A/dm², temperature 40 °C.

EXAMPLE 2

0044Profiled items made from shock-resistant polystyrene are etched in accordance with the method described in Example 2.

0045After etching, items are rinsed with water and treated for 2 minutes in a solution containing 0.01M Bi(No₃)₃ and 0,03M HNO₃ under room temperature. Afterwards, the items are rinsed in water and treated for 30 seconds in a sulphide solution which contains 0.1M Na₂S.

0046After treatment, the items arc rinsed with distilled water, dried and nickel-plated for 15 minutes in Watts' electrolyte, as described in Example 1.

EXAMPLE 3

0047Plates of ABS plastic with surface area of 50 cm² are etched for 5 minutes at room temperature solution containing 13M H₃PO₄ and 0.5M K₂S₂O₈.

0048After etching, the plates are rinsed with water and treated for 10 minutes in a solution containing 0,25M CoCl₂ and 0.7M triethanolamine under room temperature. Following this, the plates are rinsed with water, the alkalinity of which is brought to pH 9.0 by Na₂CO₃, and treated for 30 seconds in a sulphide solution which contains 0.01M sodium sulphide under room temperature.

0049After treatment, the items are rinsed with distilled water, dried and for 15 minutes nickcl-plated in Watts' electrolyte, as described in Example 1.

EXAMPLE 4

0050ABS plastic plates are etched for 5 minutes at room temperature in a solution, containing 13M H₃PO₄ and 0.5M K₂S₂O₈.

0051After etching, plates are rinsed with water and treated for 2 minutes in a solution containing 0.3M bismuth acetate and 0.35M acetic acid, at room temperature. After this, plates are rinsed in water and for treated for 30 seconds in a sulphide solution which contains 0.01M Na₂S, at room temperature.

0052After treatment, the items are rinsed with distilled water, dried and nickel-plated for 15 minutes in Watts' electrolyte, as described in Example 1.

EXAMPLE 5

0053ABS plastic plates are etched for 5 minutes in a solution at room temperature, containing 13M H₃PO₄ and 0.5M K₂S₂O₈.

0054After etching, plates are rinsed with water and treated for 2 minutes in a solution containing 0.005 Bi(NO₃)₃ and 0.01M HNO₃ at room temperature. After this, plates are rinsed in water and treated for 30 seconds in a sulphide solution which contains 0.01M Na₂S at room temperature.

0055After treatment, the items are rinsed with distilled water, dried and nickel-plated for 15 minutes in Watts' electrolyte, as described in Example 1.

EXAMPLE 6

0056ABS plastic plates are etched for 5 minutes in 60 °C solution, containing 3.8M H₂SO₄ and 3.8M CrO₃.

0057After etching, plates arc rinsed with water and treated for 10 minutes in a solution, containing 0.01M CoF₃ and 0.04M monoethanolamine, at room temperature. After this, plates are rinsed in water, brought to alkalinity of pH 14 by NaOH and treated for 30 seconds in a sulphide solution which contains 0.25M K₂S at room temperature.

0058After treatment, the items, are rinsed with distilled water, dried and nickel-plated for 15 minutes in Watts' electrolyte, as described in Example 1.

EXAMPLE 7

0059ABS plastic plates are etched for 5 minutes in 60 °C solution, containing 3.8M H₂SO₄ and 3.8M CrO₃.

0060After etching, plates are rinsed with water and treated for 2 minutes in a solution,, containing 0.01M BiCl₃ and 0.03M HCl, at room temperature. After this, plates are rinsed in water and treated for 30 seconds in a sulphide solution which contains 0,25M K₂S at room temperature.

0061After treatment, the items are rinsed with distilled water, dried and nickel-plated for 15 minutes in Watts' electrolyte, as described in Example 1.

0062Data about coating qualities are given in Table 1 below. Data shown in Table 1 below indicate that under different dielectric items and different regimes of their etching, the new method of producing coatings is not longer and the quality of the coating is not inferior to that obtained by known methods, while in some cases the quality of the now method coating is indeed superior. <tables id="tabl0001" num="0001"><img file="EP1174530A2_D0001.tif" /></tables>

0063The foregoing description of the invention is merely illustrative thereof, and it is understood that variations and modifications can be effected without departing from the spirit or scope of the invention as set forth in the following claims.