Method of producing conductor layers on dielectric surfaces

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DESCRIPTION

Procedure for the production of conductive layers on dielectric surfaces.

Background of the invention

1. Field of the invention

The present invention relates to modifying the qualities of a dielectric surface, in particular to convert a dielectric surface to be an electrical conductor. The invention can be used, for example, in various areas of industry for the preparation of dielectric surfaces for electrometallizing, especially for nickel plating. Dielectric articles that are metal-coated by methods of the invention can be used, for example, when a decorative or protective function is required, to manufacture pressed forms using the electroplating process, or for electromagnetic emission shield assemblies.

2. Background

A certain existing process for producing conductive surfaces is known (USSR patent No. 980858, B 05 D 5/12 1982), in which the dielectric surface is treated by amine-copper saline solution, then immersed in water, then in sulfur solution and then rinsed with water.

Using this procedure, a quality conductive surface can be obtained by repeating the sequence of operation 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.

Furthermore, another existing process for producing copper sulfide conductive surfaces is known (USSR patent No. 1762454, H 05 K 3/42, 3/18, 1991), in which dielectric articles are immersed in univalent cupric salt solution , then in a 0.0025 / 0.025 solution of potassium persulfate, iodine or potassium nitrite solution, then they are rinsed with water and immersed in an alkali metal sulfide solution. This process is carried out at room temperature and each operation is repeated twice.

The drawbacks of the process described in USSR Patent No. 1762454 are the same as the drawbacks described in the preceding patent. Furthermore, through the application of both existing procedures, it is impossible to leave an isolated part of the article uncovered, that is, it is impossible to achieve a selective conductive coating.

See also the Republic of Lithuania patent application No. 98-161, published in the official gazette of the Lithuanian State Patent Office (VPB) No. 5 in 2000. This filed procedure also has notable drawbacks, including the use problematic of a cobalt solution.

US-A-5 484 518 describes a process for electrometallizing by coating a substrate with a liquid dispersion of conductive particles. WO-A-00 29646 describes a process for the metallization of a plastic surface using a Co, Ag, Sn or Pb solution treatment, and a sulfide solution treatment.

It would be desirable to have new procedures for converting an electrically conductive surface.

The present invention, in its various aspects, is as set forth in the appended claims.

Summary of the invention

The present invention enables the selective production of quality conductive metal sulfide coatings on a dielectric surface without the use of ammonium hydroxide or amine, and to make the process shorter.

The invention also makes it possible to produce conductive coatings with the use of stable ionic solutions.

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

Before treatment with a bismuth composition, a dielectric substrate is suitably etched. A variety of stripping agents can be employed. An acidic aqueous solution comprising, for example, KIO is generally preferred.₄, okay₂S₂OR₈ and CrO₃.

A variety of sulfur compositions can also be employed. Generally, an aqueous solution containing a sulfur salt is preferred, for example an aqueous solution of sodium or potassium sulfide.

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The processes of the invention enable the selective production of a quality metallic sulfide conductive coating on a dielectric surface without using ammonium hydroxide, amines or other compounds that form strong complex compounds with heavy metals. Furthermore, the processes of the invention produce conductive coatings using a solution of metal ions that are highly stable. That is, in contrast to the prior systems, the bismuth treatment compositions of the invention are highly stable for prolonged periods. See, for example, the results set forth in Table 1 below.

The invention also includes articles having a metal plate thereon produced in accordance with the procedures described.

The methods and articles of the invention are useful for a wide variety of applications, including for forming electrical and conductive circuits such as those present on a printed circuit board or other electronic packaging substrate, metallic finishing, and other applications such as producing electromagnetic shields. The methods of the invention are particularly useful for depositing a decorative or protective nickel plate, or other decorative or protective metallic layer.

Other aspects of the invention are described below.

Detailed description of the invention

The invention provides new processes for metallizing dielectric substrates, particularly polymeric substrates such as, for example, ABS (acrylonitrile butadiene styrene) copolymeric substrates, epoxy resin substrates, polyetherimide substrates.

The methods of the invention generally include the use of a bismuth treatment step. Post-treatment with a sulfide material or composition enables quality metallization of the substrate, for example, with an electrolytic plating composition solution with nickel, copper, gold, silver, platinum or other metal. In contrast to other prior systems, plating catalysts such as Pd, or Pd / tin, platinum or other metal do not have to be used to deposit the metallic layer. Furthermore, unstable treatment solutions such as cobalt do not have to be employed.

To enhance metallic deposits on the dielectric substrate, preferably the dielectric substrate is first treated with an etching agent 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 alkaline permanganate compositions.

Treatment compositions employed in accordance with the invention can be applied to a dielectric substrate by a variety of procedures, including by spray application as well as dipping. Typically a composition in the form of a solution is applied to a substrate.

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

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

After treatment with the bismuth composition, the substrate is then treated with a sulfide composition, preferably an aqueous solution containing a sulfide species, for example a sulfur salt such as Na2S or K2S, or an organic sulfide, such as an alkyl sulfide. N2S or K2S is generally preferred.

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

Treatment times of a dielectric substrate with the above compositions can vary quite widely. In general, treatment times of 0.25 to 10 minutes are suitable, more typically 0.5 to 1, 2, 3, 4 or 5 or more minutes.

Preferably, a treated dielectric substrate is rinsed with water between treatment steps, ie, after etching, after bismuth treatment, and after sulfur treatment. The substrate can be properly dried prior to plating.

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A variety of metals can be metallized onto a dielectric substrate. Metallizing compositions are commercially available. For example, suitable copper, nickel and gold electrolytic plating compositions are available from the Shipley Company (Marlborough, Massachusetts). A preferred nickel electroplating composition and the procedure for using the same are set forth in the following examples. See also, Coombs, Printed Circuits Handbook (3rd Edition, McGraw Hill), incorporated herein by reference, for additional plating compositions and uses thereof.

Preferred copper plating compositions for use in accordance with the invention include an acusa composition containing an aqueous solution of CuSO₄ 5H₂Or at a concentration of 60 g / l; H₂SW₄at a concentration of 225 g / l; and Cl ions at a concentration of 50 ppm. The treated substrate to be metallized is suitably immersed in an air-stirred plating tank equipped with multiple cathode bars and a rectifier and charged with said copper plating solution. During plating, the following deposition conditions are suitably employed; 14.5 mA / cm current density²; the DC wave was DC; and a plating bath temperature of 25 ° C.

References herein to material solutions include flowable materials where all solid components are dissolved therein, as well as flowable compositions where one or more of the added components are dispersed or otherwise not completely dissolved in the fluid. Preferably, most or all of the added components are completely dissolved in the fluid vehicle (typically water).

The following non-limiting examples are illustrative of the invention.

General comments to the examples

In the following examples, products made of dielectric plates made of ABS plastic (a copolymer of vinyl cyanide, divinyl and styrene) are etched for 5 minutes at room temperature in a solution containing H₃PO₄ 13 M and K₂S₂OR₈ 0.5 M or etch for 5 minutes at 60 ° C in a solution containing H₂SW₄ 3.8 M and CrO₃ 3.8 M and rinse with water.

In the following examples, the dielectric shock resistant polystyrene (SAPS) products are stripped for 5 minutes in a solution containing H₂SW₄ 17M and KIO₄ 0.5M at room temperature and rinsed with water.

After pickling, the products are treated for 2 minutes in a solution containing Bi (NO₃)₃ or BiCl₃or Bi (CH₃COO)₃ 0.005 / 0.300 M and HNO₃ or HCl or CH₃0.01 / 0.35 M COOH, at room temperature. After this, the products are rinsed with water and for an additional 30 seconds they are treated in a solution containing Na₂ S or K₂S 0.01 / 0.25 M at room temperature.

When the procedure is complete, the items are rinsed with distilled water, dried and nickel plated for 15 minutes in Watts electrolyte containing NiSO.₄ 1 / 1.2 M; NiCl₂ 0.15 / 0.2 M and H₃BO₃ 0.4 / 0.5 M, initial flux density 0.3 A / dm² which, over the course of the nickel plating from the point of contact, increases to 3 A / dm², at the electrolyte temperature of 40 ° C.

The stability of the metal ion solution is evaluated by examining the presence of sediment in the solution (which means that the solution is unstable) or its absence (which means that the solution is stable).

The smoothness of the conductive sulfide coating is visually evaluated immediately after treatment, in sunlight, using two parameters: smooth, not smooth.

The electrical conductivity of the coating is evaluated by the rate of expansion of the electroless nickel coating from the point of contact, in centimeters per minute.

The possibility of selectively producing a conductive coating on a dielectric article is evaluated by examining whether the insulated part of the article is nickel-plated or not.

In the following Examples 1 to 7, Examples 1, 3 and 6 are for control purposes, while Examples 2, 4, 5 and 7 have been prepared according to the proposed procedure, in different concentrations of component ions of bismuth , and using different technological means.

In Examples 3, 4, 5, 6 and 7, ABS plastic plates with a surface area of ​​50 cm are treated.², while in Example 2 there are profiled articles made of impact resistant polystyrene (SAPS) with a surface area of ​​70 cm².

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Example 1

Profiled items made of impact resistant polystyrene, with a surface area of ​​70 cm², record for 5 minutes at room temperature with H₂SW₄17 M and KIO₄ 0.5 M

Items are rinsed with water after etching and treated for 10 minutes in a solution containing CoF₃ 0.01 M and NH₄OH 0.35 M, at room temperature. After this, the articles are rinsed in acetic acid to pH 5 in acidic aqueous solution and treated for 30 seconds in a sulfur solution containing 0.1 M Na2S.

After treatment, the articles 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 flux density 0.3 A / dm², temperature 40 ° C.

Example 2

Profiled articles made from impact resistant polystyrene are engraved according to the procedure described in Example 2

After etching, the articles are rinsed with water and treated for 2 minutes in a solution containing 0.01 M Bi (No3) 3 and 0.03 M HNO3 at room temperature. The items are then rinsed in water and treated for 30 seconds in a sulphide solution containing Na₂S 0.1 M.

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

Example 3

ABS plastic plates with surface area of ​​50 cm² are recorded for 5 minutes at room temperature in a solution containing H₃PO₄13 M and K₂S₂ OR₈ 0.5 M.

After etching, the plates are rinsed with water and treated for 10 minutes in a solution containing CoCl₂ 0.25 M and 0.7 M triethanolamine at room temperature. After this, the plates are rinsed with water, the alkalinity of which is brought to pH 9.0 by Na₂CO₃, and are treated for 30 seconds in a sulfide solution containing 0.01 M sodium sulfide at room temperature.

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

Example 4

ABS plastic plates are etched for 5 minutes at room temperature in a solution containing 0.5 M H3PO4 HMy & SM

After etching, the 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, the plates are rinsed in water and treated for 30 seconds in a sulfide solution containing 0.01 M Na2S, at room temperature.

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

Example 5

ABS plastic plates are etched for 5 minutes in a solution at room temperature, containing 0.5 M H3PO4 HMy & SM

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

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

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Example 6

ABS plastic plates are etched for 5 minutes at 60 ° C in a solution containing H₂SW₄ 3.8 M and CrO₃ 3.8 M

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

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

Example 7

ABS plastic plates are etched for 5 minutes at 60 ° C in a solution containing H₂SW₄ 3.8 M and CrO₃ 3.8 M

After etching, the plates are rinsed with water and treated for 2 minutes in a solution containing 0.01 M BiCl3 and 0.03 M HCl, at room temperature. After this, the plates are rinsed in water and treated for 30 seconds in a sulfide solution containing 0.25 M K2S at room temperature.

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

Data on coating qualities are given in the following Table 1. The data shown in the following Table 1 indicates that in different dielectric articles and different regimes of their etching, the new process for producing coatings is no longer and the quality of the The coating is not inferior to that obtained by known procedures, while in some cases the quality of the coating by the new procedure is in fact superior.

(Table goes to next page)

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