Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-06-14
2001-08-14
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C205S163000, C205S167000, C427S215000, C427S220000, C427S222000, C427S430100, C427S443100, C428S404000, C428S406000, C428S407000, C428S936000
Reexamination Certificate
active
06274241
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a substrate, a method of nucleation, a powder, and a method for metal plating.
BACKGROUND INFORMATION
Metal layers on a wide variety of substrates are used for applications in the electronics and electrical industry. Electroless metal plating is a valuable method of applying metal layers to such substrates regardless of the geometry or conductivity of the substrate. This method is described, for example, by Frederic A. Lowenheim: “Modern Electroplating,” John Wiley & Sons, New York, and by Heinz W. Dettner, J. Elze:
Handbuch der Galvanotechnik Band II
(Handbook of Electroplating) Carl Hauser Verlag, Munich.
In electroless metal plating, the surface of the substrate to be metal plated is provided with nucleating seeds of the noble metal. Conventionally, this is accomplished in particular by reacting compounds containing Sn
2+
with compounds containing Pd
2+
according to the equation
Sn
2+
+Pd
2+
→Sn
4+
+Pd
Palladium may be in the form of an aqueous PdCl
2
solution or an organic palladium solution into which the substrate is dipped or with which the substrate is sprayed or printed. The palladium is bound to the substrate by adsorption. In addition to palladium, platinum is also used as a nucleating metal, but palladium is preferred because of its lower price. Then at least one metal is chemically deposited on the nucleation layer by reducing one or more salts of the metal(s) to be deposited.
One disadvantage of conventional method is that it is difficult to achieve a uniform nucleation. To ensure that the nucleation layer is closed, a large quantity of nucleating metal relative to the substrate surface area is necessary in any case. Furthermore, electroless metal plating of powders has not been known in the past. It has been determined that coverage was very irregular when using the conventional method of nucleation and a subsequent electroless metal plating.
SUMMARY OF THE INVENTION
Substrates with the noble metal salt chemically bound to the substrate surface, are coated with a uniform, mostly closed nucleation layer. The thickness of this layer amounts to a maximum of a few layers of atoms. Therefore, the consumption of nucleation material is low per unit of area. In a subsequent metal plating, only a relatively small amount of metal is therefore necessary to ensure a uniform, mostly closed metal layer. It is advantageous if a group X—(K)
m
capable of bonding is bonded with residue X to the substrate surface by at least one oxygen bridge for the purpose of bonding the nucleation layer, and if group K is capable of complexing the noble metal salt, where m is an integer between 1 and 3, preferably 1. X is preferably selected from the group of silanyl moiety, hydrocarbon moiety, zirconyl moiety, titanyl moiety and moiety containing aluminum. Functional groups K which are especially suitable include a &pgr; function such as an alkenyl, alkynyl or aryl group, which may optionally be substituted, or an amino group. The present invention can be applied in an advantageous manner to oxidic substrates and substrate materials capable of forming an oxide film on the surface, in particular substrate materials selected from the group of glass, ceramics, nitride, oxynitride, carbide, silicide, zirconium oxide, nickel oxide, aluminate, aluminum oxide, plastics and combinations of two or more of these materials. It is also advantageous that the present invention can also be employed when the nucleated substrate is in the form of a powder with a particle size in the range between approximately 100 nm and approximately 300 &mgr;m. One of the advantages of the present invention is that controlled nucleation can be performed not only on whole flat substrates but also on powders, and thus controlled metal plating is also possible. A very fine, uniform distribution of the noble metal nucleation on the substrate surfaces can be achieved in particular by complexing. The noble metal is preferably a metal of group VIIIB, especially palladium or platinum, but palladium is most preferred because it is less expensive than platinum.
The method where the noble metal salt is chemically bound to the substrate surface, is suitable in particular for producing the nucleated substrate according to the present invention. It is advantageous here if the noble metal salt is bound to the substrate by the mediation of a compound that is at least bifunctional and can enter into a reaction with the substrate surface on the one hand and with the noble metal salt on the other hand. It is also advantageous if an oxidic substrate surface or a substrate surface coated with an oxide film is made to react with a compound of the general formula (A)
n
—X—(K)
m
, where A is a reactive group that can react with the hydrate shell on an oxide to form an oxygen bridge to the X group, K is a group that complexes the noble metal, and n and m are integers between 1 and 3, with n and m most preferably each being 1, i.e., the compound is bifunctional, and then it is reacted with a soluble complex noble metal compound capable of ligand exchange with the K group, and the salt is optionally reduced in a known manner. It is preferable if X and K have the same meanings as in the group X—(K)
m
(discussed above), and A is selected from the group of halogen, ester group, carboxyl group and acid halide group. Advantageous representatives of the above-mentioned compound are selected from the group of allyldimethylchlorosilane, oleic acid or linoleic acid, naphthenic acids and aminopropylmethyldiethoxysilane.
In carrying out this method, it is advantageous if the noble metal salt used in the process is complexed with a complexing agent such as cyclooctadiene or benzonitrile which is capable of ligand exchange with the functional group K. To improve the adhesion of the nucleation material and to facilitate the reaction of the substrate surface with the bifunctional compound, it is advantageous if the substrate is treated before nucleation with digestion agents such as alkali metal hydroxide, in particular with sodium hydroxide or solutions containing hydrofluoric acid such as a hydrofluoric acid solution or solutions containing HF/NH
4
F mixtures. The method according to the present invention can be used when the substrate material is selected from one of the above-mentioned materials.
With the present invention it is possible to provide a nucleated powder which is coated with a metal layer. The powder according to the present invention has advantageous properties if the nucleation is chemically bound to the powdered surface, and in order to bind the nucleation layer it is advantageous if a group X—(K)
m
that is capable of binding is bound with the group X to the substrate surface by at least one oxygen bridge, and the functional group K is capable of complexing the noble metal salt, with m being an integer between 1 and 3, preferably 1. It is advantageous if X is selected from the group of silanyl moiety, hydrocarbon moiety, zirconyl moiety, titanyl moiety and moiety containing aluminum. Especially suitable functional groups K would include a &pgr; function such as an alkenyl, alkynyl or aryl group, which could optionally be substituted, or an amino group. It is advantageous if the powder material is a material which is coated with a hydrate shell such as glass, ceramic, nitride, oxynitride, carbide, silicide, zirconium oxide, nickel oxide, aluminate, aluminum oxide, plastic or a combination of two or more of these material, but class and ceramic are especially preferred. It is advantageous if the metal layer contains an alloy such as Ni/W, Ni/Sn, Co/W and Co/Mo, a single metal such as Ni, Cu, Ag, Au and platinum metals, or metal oxide(s) such as Cu and Cu
2
O.
In sintering the metal plated powder according to the present invention, a two-phase material with a continuous conductive phase is formed. The electric resistance is adjusted on the basis of the proportion by volume of the conductive metal phase which develops a type of network. Therefore,
Brinz Thomas
Eisele Ulrich
Kling Dorothee
Weber Lothar
Kenyon & Kenyon
Le Hoa T.
Robert & Bosch GmbH
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