Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2002-11-21
2004-09-28
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S427000, C075S428000, C075S429000, C075S430000, C075S432000, C075S714000, C075S743000, C075S744000
Reexamination Certificate
active
06797033
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a method of recovering catalytic metals. More specifically, the present invention is directed to a method of recovering catalytic metals from fluid compositions containing catalytic metal colloids.
Electroless metal deposition refers to the chemical deposition of a metal on a conductive, non-conductive, or semi-conductive substrate in the absence of an external electric source. Electroless deposition is used for many purposes, for example, in the manufacture of printed circuit boards where, in one method, an electroless metal, often copper, is deposited on a dielectric substrate either as a uniform surface coating or in a predetermined pattern. The initial electroless copper deposit is thin and may be further built up by electroplating or may be deposited directly to full thickness.
The substrate over which an electroless metal deposit is formed is often a plastic panel which may have a metal foil such as copper laminated to one or both of its surfaces, for example, with adhesive, to form a metal clad substrate. Where both surfaces of the substrate are to be used, connections are provided therebetween by means of holes through the panel at appropriate locations. The walls of the holes are made conductive with electroless coating.
The electroless deposition of a metal on either a metallic or non-metallic substrate requires pretreatment or sensitization of the substrate to render it catalytic to reception of a metal deposit. Catalytic metal colloids are often used as the sensitizer or seeder to prepare the substrate for reception of the metal.
Catalytic metal colloids are dispersions formed by the admixture of a catalytic metal ion and a non-catalytic metal ion in an amount in excess of the catalytic metal ion. Such dispersions are often formed in acidic solutions but also may be formed in alkaline solutions. Suitable catalytic metal ions are well known in the art. Examples of highly desirable catalytic metal ions are the noble metal ions of gold, platinum and palladium. An example of a suitable non-catalytic metal ion used to form the metal colloid is stannous ion. Colloidal baths or solutions may contain tin in amounts of from about 10 to about 50 or more times than the amount of catalytic metal. Typically, a catalytic metal such as palladium may range in concentrations of from about 140 ppm to about 150 ppm in the colloidal bath. Such catalysts are commercially available. U.S. Pat. No. 3,011,920 to Shipley, Jr. discloses methods of making such catalysts, the disclosure of which is hereby incorporated in its entirety herein by reference. Also, U.S. Pat. Nos. 4,020,009 and 4,085,066 both to Gulla and assigned to Shipley Company, Inc. disclose catalytic metal colloids and methods of making the same, the disclosures of which are hereby incorporated in their entireties herein by reference.
Prior to electroless metal deposition on a substrate, such as a printed circuit board, the part of the substrate to be plated is immersed in a colloidal bath or solution. The substrate is then rinsed with water and then placed in an electroless bath for plating. About 70% or more of the catalyst consumed by the substrate during immersion is washed off of the substrate by the rinse or dragout bath. Thus, about 30% or less of the catalyst remains on the substrate. The catalytic metal colloids represent a major cost in electroless metal deposition. Thus, recovering the catalytic metal colloids for reuse is highly desirable. However, recovery of the catalytic metal from the rinse or dragout bath is difficult because the catalytic metal is in small concentrations and the non-catalytic metal, such as tin, is present in large concentrations. Thus, the rinse is often discarded with the loss of the valuable catalytic metal.
In addition to the loss of catalytic metal from rinses, catalytic metals also may be lost from the catalytic metal colloidal solutions or baths. For example, when employing copper clad substrates, such as printed circuit boards, which are drilled to provide through-holes, the through-holes are metal plated to provide a continuous current path when individual boards are joined together. Because the exposed surfaces in the holes are non-metallic, electroless plating techniques including the step of catalyzing by means of a catalytic metal colloid, such as tin/palladium colloid catalyst, is employed. Copper clad boards are immersed in the catalytic bath to deposit the catalyst thereon. Copper from the copper clad boards contaminates the catalytic metal colloidal bath with continued use of the bath. When the contamination reaches an extent such that the bath becomes ineffective or the electroless plating becomes less adherent than desirable, the bath is “spent” and is then discarded as waste.
Because many of the metals employed in the catalytic metal colloids are costly, especially gold, platinum and palladium, industries, such as the printed circuit board industry, would prefer to recover the metals rather than dispose of them. Recovery of the metals would reduce manufacturing costs to manufacturers of printed circuit boards and reduce costs to the manufacturers' customers. Also, the catalytic metals present a hazard to the environment, and disposal of the metals is strictly regulated by the Federal and State governments. Often large volumes of liquid waste are transported far distances to designated sites for proper disposal. Thus, proper disposal procedures for the metals are costly to the industry and much of the cost is passed onto the customer. Although recovery of catalytic metals from catalytic metal colloids is highly desirable, an economically efficient method for the recovery of the catalytic metal from colloids has not been developed. Accordingly, there is a need for an economically and environmentally safe method for recovering catalytic metals from colloidal metal catalysts.
A few attempts have been made to recover catalytic metals from waste solutions. U.S. Pat. No. 4,435,258 to Milka, Jr. et al. and assigned to Western Electric Co., Inc. discloses a method of recovering palladium from spent electroless catalytic baths employing an electrolytic cell. The method of recovery disclosed in the '258 patent involves (a) dissolving tin/palladium colloid in a spent catalytic bath with an oxidizing agent such as hydrogen peroxide to form a true solution; (b) heating the bath to a temperature and for a time sufficient to essentially remove excess hydrogen peroxide; (c) placing the solution in an electrolytic cell having (1) a nickel anode, and (2) a cathode composed of a metal or metallic surface, such as copper or nickel, for the palladium to be deposited; and (d) electrodeposition of palladium from the solution onto the cathode at a voltage that allegedly tends to minimize and substantially reduce tin deposits. There are many disadvantages with such a method. Electrolytic cells can be costly. The consumer of the palladium colloid either has to invest in purchasing such electrolytic cells, or pay the cost of transporting the spent catalytic bath to a site where the electrolytic cell is located. Because of the weight of fluids, the cost of transporting the bath to the recovery site is expensive. If the consumer purchases the electrolytic cell, then the consumer must expend funds in both operating and maintaining the cell. Such an electrolytic cell as described in the '258 patent is specially designed and replacement of worn parts may not be inexpensive or readily obtainable. For example, the electrolytic cell of the '258 patent has a specially designed cascading structure to allegedly prevent deposited palladium from breaking away from the cathode. Also, a high purity nickel anode and cathode are recommended to obtain acceptable recovery amounts of palladium. Such adds to the cost of the apparatus. Amounts of palladium recovered also depend on the amounts of specific components in the colloidal bath as well as any contaminants. The more dilute the palladium and the more contaminants in the bath the
Bohling James C.
Doubrava Jeffrey
Gallegos Anthony
Lundquist Eric G.
Serell Chad
Andrews Melvyn
Piskorski John J.
Shipley Company L.L.C.
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