Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2000-02-23
2002-04-16
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S282000
Reexamination Certificate
active
06372055
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to adhesion promoting baths. In particular, this invention relates to a method for replenishing adhesion promoting baths for use in circuit board manufacture.
Multilayer printed circuit boards are used for a variety of electrical applications and provide the advantage of conservation of weight and space. A multilayer board is comprised of two or more circuit layers, each circuit layer separated from another by one or more layers of dielectric material. Circuit layers are formed by applying a copper layer onto a polymeric substrate. Printed circuits are then formed on the copper layers by techniques well known to the art, for example print and etch to define and produce the circuit traces—i.e., discrete circuit lines in a desired circuit pattern. Once the circuit patterns are formed, a stack is formed comprising multiple circuit layers separated from each other by a dielectric layer, typically epoxy or epoxy/glass. Once the stack is formed, it is subjected to heat and pressure to form the laminated multilayer circuit board.
Following lamination, the multiple circuit layers are electrically connected to each other by drilling through holes through the board surface. Resin smear from through-hole drilling is removed under rather stringent conditions, for example, by treatment with a concentrated sulfuric acid or hot alkaline permanganate solution. Thereafter, the through-holes are further processed and plated to provide a conductive interconnecting surface.
Prior to lamination and through hole formation, the discrete copper circuit lines are typically treated with an adhesion promoter to improve bond strength between each circuit layer and adjacent interleaving dielectric resin layers. One method used in the art to improve bond strength involves treatment of the circuit layer with compositions containing an acid, an oxidant, a corrosion inhibitor and typically one or more additional components to provide a micro-roughened, conversion coated surface. Such micro-roughened and conversion coated surfaces enhance adhesion and wettability to the adjacent insulating layer by a mechanism that is believed to include mechanical interlocking between the metal surface and a dielectric resin layer. Metal surfaces that have been micro-etched, but not conversion coated do not generally possess as high a degree of surface roughness and texture, as can be inferred from their greater reflection of visible light or from scanning electron micrographs.
The adhesion promotion baths may be run horizontally or vertically and are typically run continuously. During continuous operation of the bath, the components of the bath are depleted and makeup components are added periodically. In order to provide the appropriate conversion coated surface, the makeup components must be added in amounts sufficient to maintain the components of the bath within a given range and ratio to each other. Typically, makeup solutions are provided which contain mixtures of the bath components in predetermined amounts and ratios. As the adhesion promotion bath is run, precipitation of material from solution may occur. Such precipitate may be removed by various methods, such as filtration. The makeup solutions generally account for components depleted due to such precipitate formation.
Periodically, the adhesion promotion bath must be shut down for a period of time, such as for 6 to 12 hours or over a weekend. During such a shut down, a failure of the bath may occur, i.e. an amount of precipitate may form that far exceeds the normal level. Such bath failure is more likely to occur when the copper concentration is greater than about 10 grams per liter. When such a bath is started up again after such a shut down, makeup solutions are typically added, however the resulting coatings often have unacceptable color and peel strength. At this point, the bath is usually discarded and a fresh bath is prepared, which greatly adds to the time and cost of the process.
In U.K Patent Application No. 2,203,387, a copper etching process is described with an etch bath regeneration step. A hydrogen peroxide etching composition comprising stabilizers for the peroxide, sulfuric acid and less than about 0.2% of an organic additive selected from ethylene glycol, propylene glycol and gum arabic. The organic additive functions to control the crystallization of copper sulfate on the sides of the etchant bath during cooling of the bath.
U.S. Pat. No. 5,800,859 (Price et al.) discloses a method for providing a micro-roughened conversion coated metal surface by contacting the metal surface with an adhesion promoting composition containing hydrogen peroxide, an inorganic acid, an organic corrosion inhibitor and a surfactant. Price et al. do not disclose the need for replenishing adhesion promoting baths, nor the problem of bath failures on start up after an extended shut down.
U.S. Pat. No. 5,352,350 (Andricacos et al.) discloses a method for maintaining a constant chemical composition in solutions used for wet chemical processing, particularly plating baths, i.e. a steady state maintenance of the baths. Such method performs a material balance on each component using the stoichiometry of chemical reactions in the bath to predict the amount of each component consumed and then adding a predicted amount of each component to the bath. This patent does not recognize the problem of bath failure on start up after an extended shut down.
Thus, there is a need for extending the service life of adhesion promoting baths that allows for easy start up of a bath after an extended shut down without the need to prepare a new bath.
SUMMARY OF THE INVENTION
It has been surprisingly found that adhesion promoting baths can be replenished, or their service life extended, following a failure upon start up of the bath after an extended shut down by the addition of a sufficient amount of corrosion inhibitor.
In one aspect, the present invention provides a method of replenishing an adhesion promoting bath including an acid, an oxidizer, a corrosion inhibitor and optionally, one or more additional components, after an extended shut down, including the steps of adjusting the concentration of acid, oxidant and optional components to working levels and adding a sufficient amount of corrosion inhibitor to provide conversion coated substrate surfaces having sufficiently dark color and peel strength.
In a second aspect, the present invention provides a method for providing a micro-roughened conversion coated metal surface comprising contacting the metal surface with the replenished adhesion promoting bath described above.
DETAILED DESCRIPTION OF THE INVENTION
As used throughout this specification, the following abbreviations shall have the following meanings, unless the context clearly indicates otherwise: g=gram; mg=milligram; mL=milliliter; L=liter; DI=deionized; C=Centigrade; lbf=pound force; in=inch; psi=pounds per square inch; ppm=parts per million; and wt %=percent by weight.
The term “alkyl” refers to linear, branched and cyclic alkyl. “Halide” refers to fluoride, chloride, bromide, and iodide. The terms “printed circuit board” and “printed wiring board” are used interchangeably throughout this specification. All amounts are percent by weight and all ratios are by weight, unless otherwise noted. All numerical ranges are inclusive.
The present invention is directed to a method of replenishing or rejuvenating an adhesion promoting bath after a failure event. The term “failure” or “failure event” refers to the start up of an adhesion promoting bath after an extended shut down period where the resulting metal surfaces do not have sufficiently dark color or peel strength to be useful in the printed wiring board industry.
In general, the etching and adhesion promoting baths of the present invention comprise oxidizer, acid, corrosion inhibitor, and optionally one or more additional components. It is preferred that the adhesion promoting baths of the prese
Bayes Martin W.
Couble Edward C.
Montano Joseph R.
Wynja Kimberly B.
Cairns S. Matthew
Oltmans Andrew L.
Sheehan John
Shipley Company L.L.C.
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