Selective fiber metallization

Details Selective fiber metallization Selective fiber metallization

2000-11-02

2002-03-12

Barr, Michael (Department: 1762)

Coating processes

Optical element produced

Polarizer, windshield, optical fiber, projection screen, or...

C427S264000, C427S271000, C427S404000, C427S437000, C427S438000, C427S443100, C427S434600, C427S304000

Reexamination Certificate

active

06355301

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to electroless deposition of metal layers on non-conducting, generally amorphous substrate materials and more particularly to selective deposition of metal on fibrous structures using a process to deactivate catalytic species in selected areas not requiring deposition of electroless metal.
BACKGROUND OF THE INVENTION
Methods for electroless deposition of metals on a variety of substrate materials have been known since the earliest use of aldehydes to precipitate silver from solutions containing silver salts. More recently, the use of electroless plating methods has received attention following the discovery that some alloys, such as electroless deposited nickel phosphorus alloys, possess unique properties, and because of the growing use of such methods for plating plastics, and manufacturing optical, electronic and optoelectronic devices. Optical communication represents an area of use wherein selective coating of metal on glass facilitates hermetically sealed soldered connection of optical fiber ends to ferrule bodies.
Electroless plating solutions usually contain a metal salt, a reducing agent, a pH adjuster, a complexing agent, and one or more additives to control properties including bath stability, film properties, and metal deposition rate. An ideal electroless plating solution deposits metal only on an immersed article, never as a film on the sides of the tank or as a fine powder. All parts of an immersed article must have been thoroughly cleaned before plating. The presence of dirt or oxide on an article may either interfere with uniform deposition or lead to loss of adhesion of the metal deposit.
Application of metal to non-conductors requires the presence of a seed material in contact with the surface of a thoroughly cleaned article to provide a catalytic site for electroless metal deposition. Activation of a surface of non-conducting and dielectric materials for electroless metal plating commonly uses solutions containing acidic stannous chloride and acidic palladium chloride. The original catalysts were separate solutions with acidic stannous chloride acting as a reducing agent for subsequently applied palladium chloride to produce catalytic sites of metallic palladium at the surface of a cleaned article. It is the physical presence and chemical activity of the palladium that is a prerequisite for initiation of the electroless plating process. The two-step catalyst system may be replaced by a catalyst solution containing pre-reacted palladium and stannous chlorides.
U.S. Pat. No. 3,632,435 confirms the use of tin and palladium salts for surface activation and further includes the use of salts of other noble metals in the place of palladium. This reference also addresses deactivation or masking of selected portions of a catalyzed surface that was activated using stannous and palladium ions as previously described. Deactivation, in this case, involves the application of destabilizing agents. One category of destabilizing agents includes polyvalent hydrolysable metal ions, such as lead, iron and aluminum, which have the capacity to oxidize stannous ions to stannic ions. Stannic ions do not react with palladium solutions to produce catalytic sites of elemental palladium for deposition of electroless metal layers.
Chelating agents for noble metals include organic compounds, e.g. dibasic acids, containing acid functionality to provide another type of destabilizing agent according to U.S. Pat. No. 3,632,435. The acidic chelating agent acts primarily on the noble metal, e.g. palladium, of a catalyzed surface to mask its catalytic behavior thereby preventing electroless metal deposition in treated areas. Acid treatment may be used in other cases to facilitate electroless plating of an overcoat plating on metal conductors while preventing metal deposition on dielectric material surrounding the metal conductors. U.S. Pat. No. 5,167,992 uses a deactivator acid solution to remove noble metal ions from dielectric surfaces after treatment with solutions of noble metal salts. Suitable deactivator acids include organic acids and inorganic acids. It should be noted that an activator solution according to U.S. Pat. No. 5,167,992 contains no tin and that deactivation involves removal of ionic not elemental noble metal.
Other methods for selective electroless plating of non-conducting substrates include imagewise exposure of photoresists followed by development and activation of exposed areas of a substrate. Such methods, as taught by U.S. Pat. Nos. 3,672,925 and 4,448,804, are beyond the scope of the present invention.
The use of optical fiber signal carriers frequently involves sealing an optical fiber into the bore of an optical fiber connecting component such as a ferrule. Preferably the optical fiber becomes hermetically sealed within the component as described in U.S. Pat. Nos. 4,707,065 and 5,793,916. In each case, the optical fiber has a surface layer of metal, usually gold, suitable for bonding and sealing with a low melting metal, preferably solder.
An article published in the Proceedings of the 2000 Electronic Components and Technology Conference (Watson, J. E. et al, 2000 Proceedings. 50
th
Electronic Components and Technology Conference, May 21-24, 2000, p. 250-5.) describes the use of electroless plating for applying metal to the surface of an optical fiber. An assembly of a metallized fiber sealed into a ferrule was tested to assess the strength of the fiber and how an assembly might fail. U.S. Pat. No. 5,380,559 describes activation of a single fiber end and a plurality of optical fiber ends for more consistent electroless metal deposition using stannous fluoride instead of stannous chloride to generate catalytic sites of elemental palladium. According to the reference (U.S. Pat. No. 5,380,559), with the standard use of stannous chloride, for electroless plating, it is not possible to obtain reproducible, uniform plating of electroless nickel on silica fibers.
In view of the use of electroless plating processes for coating non-conductive surfaces with metal, and the use of such processes with optical fibers and related components, there is a need for application of electroless metal to selected areas of an optical fiber end prior to sealing a fiber into an optical connecting component using solder. The present invention has been developed as a simplified selective electroless metallizing process with improved efficiency as a further benefit to the user. These enhancements and benefits are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
SUMMARY OF THE INVENTION
This invention provides an electroless plating process for sequential surface masking and deposition of nickel and gold onto single and multiple fibers using aqueous chemistry. The process includes a sensitization of a surface of a fiber, preferably an optical fiber, using a dilute aqueous solution of stannous chloride in de-ionized water. Subsequent treatment includes immersion of the sensitized optical fiber in an aqueous solution of palladium chloride/hydrochloric acid followed by selective deactivation of the treated fiber during a second immersion of a fiber in an aqueous solution of stannous chloride. During electroless plating from commercially available electroless nickel and optionally immersion gold solutions, metal deposits only on areas of an optical fiber surface that remain activated. The formation of hermetic solder joints to the metallized fiber may be determined by helium leak testing. After soldering, solder pull-test strengths typically range from 1.4-2.3 kg (3-5 pounds), depending on the type of solder used.
For treatment of non conducting substrates, including individual fibers, especially optical fibers, the present invention provides a process for applying a metal to selected areas of a non-conducting substrate. The process comprises the steps of providing a non-conducting substrate having an uncoated portion to be treated with a sensitizer solution to provide a sensitized portion

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