Composite electroless plating

Abstract

This invention is a process for electrolessly metallizing an article to provide on the surface thereof a metal coating incorporating therein particulate matter, in which the process comprises contacting the surface of said article with an electroless metallizing bath essentially free of heavy metals, an electroless metallizing bath used in the process, and articles with coatings resulting from the process.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates in general to composite electroless plating, and more particularly, to a process of composite electroless plating without the intentional introduction of heavy metals, articles resulting from the process, and plating baths used in the process. [0002] The electroless plating of articles or substrates with a composite coating containing finely dispersed particulate matter is well documented. [0003] Electroless plating generally involves the deposition of metal alloys by chemical or electrochemical reduction of aqueous metal ions. Through such deposition, the process of electrolessly metallizing a desired metal coating over an article or substrate is achieved. [0004] The fundamentals of composite electroless plating are documented in a text entitled “Electroless Plating Fundamentals and Applications,” edited by G. Mallory and J. B. Hajdu, Chapter 11, published by American Electroplaters and Surface Finishers Society (1990...

AI Technical Summary

Benefits of technology

[0012] One possible reason for this substantial decrease in plating rate is that while hydrogen bubbles emanate from the surface of all articles being plated in all varieties of electroless baths, there is a propensity for such bubbles to cling to the surface of articles being plated in certain composite electroless baths for a longer amount of time than in a conventional electroless baths, which causes a further reduction of the plating rate. The accumulation of bubbles on the surface of articles being plated in a composite electroless bath restricts the release of depleted solution from the surface and subsequent replenishment of fresh solution to the surface that would result in renewed plating at that site.

[0013] The relatively low plating rate of certain composite electroless processes has resulted in the thickness specification for many articles treated in the processes being lower than the typical thickness specification for electroless processes without insoluble or sparingly soluble particulate matter. While the frictional and release properties of composite electroless coatings are generally independent of the coating's thickness, numerous other properties of the coating are dependent on the coating thickness such as wear resistance and corrosion resistance. Therefore, resorting to thinner composite electroless coatings inherently reduces the coating's wear and corrosion resistance and consequently has limited the extent of applications for which composite electroless coatings can be commercially utilized.

[0015] However, Applicants have found that the particulate matter stabilizers also act to prevent the decomposition of the plating baths, such that the intentional introduction of heavy metals is no longer necessary to stabilize the bath. In addition, although it was previously known that an increased concentration of heavy metals above a minimum level necessary for stabilization resulted in a reduced plating rate, Applicants unexpectedly found that a reduction of heavy metal concentration below a minimum level required for stabilization actually increased the plating rate for many types of coatings.

[0016] Accordingly, an object of the present invention is to provide a process of composite electroless plating without the intentional introduction of heavy metals, plating baths used in the process, and coatings for articles resulting from the process.

[0017] In this regard, increasingly stringent rules and regulations that restrict or prohibit the use of heavy metals, such as the End-Of-Life Vehicle (ELV) Regulations and Restriction of Certain Hazardous Substances (RoHS), mean that the present invention has an extra added benefit. Since Applicants have found that particulate matter stabilizers stabilize the plating bath as well and overcome the instability from adding insoluble or sparingly soluble particulate matter, use of the present invention complies with such regulations because it does away with the need for potentially costly and certainly environmentally hazardous heavy metals in composite electroless plating.

Problems solved by technology

However, the use of such heavy metals has drawbacks.

As explained in U.S. Pat. No. 6,306,466, increased concentration of heavy metals in electroless composite plating baths above a minimum level necessary for stabilization results in a diminished plating rate.

Therefore, resorting to thinner composite electroless coatings inherently reduces the coating's wear and corrosion resistance and consequently has limited the extent of applications for which composite electroless coatings can be commercially utilized.

In addition, the inclusion of insoluble particulate matter in composite electroless baths introduces additional instability.