Coating processes – With pretreatment of the base – Preapplied reactant or reaction promoter or hardener
Reexamination Certificate
2001-02-08
2003-04-29
Talbot, Brian K. (Department: 1762)
Coating processes
With pretreatment of the base
Preapplied reactant or reaction promoter or hardener
C427S372200, C427S388100, C427S421100, C205S210000, C205S215000
Reexamination Certificate
active
06555170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method of electroplating based on coating the surface to be electroplated with filming amines such that electroplating proceeds with greatly improved speed and efficiency, especially in low current areas.
2. Description of Related Art
The metal finishing industry utilizes many types of processes, among them the electroplating of dissimilar metals, one onto another, as well as the electroplating of similar metals. In the fabrication of circuit boards, for example, copper is plated on top of copper to selectively build up the circuits.
Regardless of the type of electroplating, the first step is cleaning the substrate metal such that little or no contamination remains to interfere with the flow of ions from the anode to the substrate metal. Contamination takes the form of oxides, greases, oils, fingerprints, and the like. The contamination must be removed and the substrate metal made sufficiently active to allow the plating function to begin. This pre-plate cleaning often takes the form of immersion in multiple hot alkaline soak solutions, followed by one or more acid soak baths to activate the metal substrate and to remove any built up oxides. Oxides form extremely rapidly during rinsing cycles between the various cleaning and activating steps, and the presence of any oxides inhibits efficient plating.
Additionally, the plating cycle itself is slow and represents one of the more time consuming and difficult steps in the production cycle. Parts with odd shapes add to the problem, because low current density areas do not plate as quickly as the rest of the part. Thus excess plating in the high current density areas results from the extended plating time and/or increased amperage needed to adequately plate the low density areas. When holes are present in the article to be plated, the deposited coating on the interior of the hole is thicker at the top and bottom of the hole than at the center of the hole. The uneven coating where the plating on the exterior of the hole is thicker than the interior of the hole is known as “dog boning”.
The throwing power of an electroplating bath is the ratio of the current flowing at the center of the hole to the current flowing at the ends of the hole. A plating bath which has high throwing power has relatively equal flow of current at the center of the hole and the ends of the hole. A bath with high throwing power would plate the interior of the hole evenly from top to bottom. Uneven plating of the interior of the hole of circuit boards can lead to defects in the circuit board. There is thus a need for a method that cleans and activates parts and facilitates rapid, uniform electroplating.
SUMMARY OF THE INVENTION
One aspect of the invention involves a method of electroplating a substrate. The method involves obtaining a solution containing from about 0.0003% to about 30% of a film forming amine and sufficient acid to produce a pH of less than about 6.5. The method also includes coating at least a portion of the substrate with the solution, thereby forming a film on the substrate; and plating the substrate.
Advantageously, the coating involves immersing the substrate in the solution. In an embodiment, the coating involves spraying at least a portion of the substrate with the solution. Preferably, the substrate is rinsed after the coating.
In an embodiment, the solution contains a plurality of film forming amines. Advantageously, the solution includes a plurality of acids. Preferably, the acid is phosphoric acid, sulfonic acid, hydroxyacetic acid, hydrochloric acid, sulfuric acid, sulfonic acid, formic acid, malonic acid, succinic acid, aspartic acid, mallic acid, acetic acid, citric acid, nitric acid, methane sulfonic acid, gallic acid, maleic acid, or fumaric acid.
Preferably, the solution is diluted to not less than about 1% of its initial concentration. Advantageously, the substrate is dried after the coating. In an embodiment, the film forming amine inhibits oxidation of the substrate. Preferably, the acid reduces the pH of the solution to below 4.
The film forming amine may be a fatty acid amine or a long chain alkylamine. Advantageously, the film forming amine is a primary amine, a secondary amine, a tertiary amine, an alkylamine, a C-8 through C-22 amine, a basic mono cyclic tertiary amine, a stabilized abietylamine, a diaminopropane, a dehydroabietylamine, or an ethoxylate, salt, or adduct thereof.
Preferably, the solution cleans the substrate. Advantageously, a resist layer is deposited on at least a portion of the film. In an embodiment, at least a portion of the resist layer is removed. The method may also include pattern plating the substrate. The substrate may also be contacted with an acid pickle solution containing a film forming amine, where the contacting is before plating. The coating of the substrate may be repeated after plating. Preferably, the substrate is plated again after repeating the coating. The plating may be performed in a solution which contains a film forming amine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The embodiments of the present invention relate to a method of electroplating in which the substrate to be electroplated can be prepared for electroplating in a single step. Further, both the speed and the efficiency of electroplating are increased with the embodiments of the method, especially in low current density areas such as the interior of holes. When an embodiment of the method was used to plate steel door hinges, the steel door hinges were plated in about a quarter of the time and with greater than ⅔ reduction in energy consumption compared to conventional plating. This is even more surprising, because the embodiments of the present invention do not activate but rather passivate metals.
The embodiments of the method include the use of a solution to prepare the substrate for electroplating. The solution comprises (1) a filming amine or combination of filming amines, (2) an acid or combination of acids, and (3) water. A surfactant can optionally be added to assist in cleaning and wetting of the substrates. The surfactant can also act as an antifoaming agent. The solution of the embodiments of the present invention may also be used as a cleaner or as a substitute for an acid pickle, where additional wetting agents are not required.
For purposes of this invention, a substrate is considered to be prepared for electroplating when the substrate is clean such that little or no contamination remains to interfere with the flow of ions from the plating solution to the substrate metal and when a layer of filming amine or a combination of filming amines is present on the surface of the substrate.
In addition, the solution may be used for cleaning and priming substrates, inner layer core materials, and flexible composite materials used in the manufacture of PCBs (printed circuit boards).
A filming amine is defined as a primary, secondary, tertiary or quaternary amine or derivatives thereof in which the group(s) attached to nitrogen are sufficient to cause a solution of the amine, when placed upon a substrate having a charge, to form a continuous layer when the pH of the solution is below 7. An acid is defined as a compound that, when placed in pure water with a pH of 7, causes the pH to drop below 7. A surfactant is defined as a compound which lowers the surface tension of the solution.
A wide variety of film forming amines can be used in the present invention. Preferable filming amines may be either cationic, amphoteric or nonionic. Neutral and anionic amines may also be used but do not tend to work well unless used with a strongly acid medium. Preferable filming amines may include, but are not limited to, fatty acid amines and long chain alkylamines. Amines used in embodiments of the method of the present invention can be prepared by methods known to those skilled in the art or may be purchased from any of a number of commercial sources. Preferable amines include, but are not limited to, primary, seconda
Duratech Industries, Inc.
Knobbe Martens Olson & Bear LLP
Talbot Brian K.
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