Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-04-10
2003-07-08
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S280000, C156S326000, C427S156000, C427S388500, C106S287140, C106S287210
Reexamination Certificate
active
06589381
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for treating metal foil to retain a clean metal foil surface. In particular, the present invention relates to a method for treating metal foil with an inert silane, titanate or zirconate compound to improve its resistance to resin dust.
BACKGROUND OF THE INVENTION
Copper clad laminates are the basic component of the printed circuit boards used in the electronics industry. In the most common processes, a copper foil is bonded to a prepreg of resin, such as epoxy resin, impregnated fiberglass by heat and pressure. The copper foil surface that is pressed against the prepreg is typically an uneven or profiled surface with some kind of additional bonding treatment applied to insure that the laminate remains together under normal processing conditions.
The opposing foil surface (the surface not bonded to the prepreg) is typically a smooth surface with various treatments that are aimed at preventing oxidation of the foil and allowing solder wettability and adequate photoresist adhesion. The opposing foil surface is often scrubbed to remove various debris prior to applying the photoresist. In particular, resin dust formed during the handling of the prepreg during lay-up of the laminate has a tendency to land on the shiny surface of the copper foil to which it may become undesirably bonded during the lamination cycle. In fact, any organic material may become undesirably bonded to metal foil during the lamination cycle. If these resin dust spots are not removed prior to etching the laminate when producing a pattern of lines and spaces of copper, then the resin spots shield portions of the copper from the etching solution and prevent its complete removal. As a result, forming fine metal lines with laminates contaminated with resin dust is difficult. If a resin dust spot is large enough and in the wrong location, it provides an unintended bridge between copper lines that would cause a short in the subsequently formed circuits and render the board useless. Etching copper clad laminates with resin dust spots, especially epoxy resin dust spots, is thus problematic.
Recently two types of metal foil are available where scrubbing of the exposed laminate surface is not practical. The first type is double treat foil for multilayer boards, where both sides of the copper foil are given an additional bonding treatment because after the first lamination, another prepreg is placed against the opposing foil surface and pressed to form a prepreg-foil-prepreg “sandwich.” Any scrubbing of this surface would damage the bonding treatment and render it less capable of forming a strong bond to the second prepreg.
The second type of metal foil is reverse treat foil, where the bonding treatment is applied only to the smooth side of the foil that, in turn, is laminated to the prepreg, leaving the uneven or matte surface exposed to the resin dust. Scrubbing of this surface is an undesirable process that reduces some of the profile desired for photoresist attachment and future processing. Scrubbing certain metal foil surfaces is disfavored.
SUMMARY OF THE INVENTION
In one embodiment, the present invention relates to a method of increasing resin dust resistance of metal foil comprising contacting the metal foil with an inert silane, titanate or zirconate compound to form a resin dust resistant film having a thickness from about 0.001 microns to about 1 micron on a surface of the metal foil.
In another embodiment, the present invention relates to a method of treating metal foil comprising contacting a first side of the metal foil with a hydrocarbylsilane solution to form a resin dust resistant film on a surface of the metal foil, the hydrocarbylsilane solution comprising from about 0.01% to about 10% v/v of a hydrocarbylsilane; and laminating a second side of the metal foil to a prepreg.
In yet another embodiment, the present invention relates to a method of treating copper foil comprising contacting the copper foil with a solution comprising from about 0.05% to about 5% v/v of an alkylsilane and from about 0.1 g/l to about 10 g/l of a triazole compound; and laminating the metal foil to a resin material.
As a result of the present invention, it is possible to provide metal foil which exhibits high resin dust resistance. In particular, the present invention provides a coating for application to a metal foil surface that prevents resin dust from sticking and/or accumulating to the exposed side of metal foil which is not adjacent a prepreg. Thus, a clean metal foil surface after lamination without scrubbing is obtainable due to the present invention. It is also possible to maintain a clean metal foil surface after lamination without scrubbing or cleaning.
DESCRIPTION OF THE INVENTION
The present invention involves treating metal foil by contacting the surface of a metal foil with an inert silane, titanate or zirconate compound to impart resin dust resistance to the metal foil. In other words, metal foil is treated by contacting the surface of a metal foil with an inert silane, titanate or zirconate compound to impart reduced resin dust adhesion to the metal foil. The silane compounds are preferred. Typically, the exposed side of metal foil is treated (the side not adjacent the prepreg). Resin dust includes various debris, particulates and other small particles which are released or emanate from the use, storage, transfer, wear and/or tear of resin articles, such as resin based dielectric materials and prepregs. Resin dust typically comes from organic materials such as epoxy resin materials, polyimide resin materials, and polyester resin materials. Resin dust from epoxy resin materials is particularly troublesome. Treating metal foil by contacting the surface of a metal foil with an inert silane, titanate or zirconate compound in accordance with the present invention forms a dust resistant film on the metal foil surface.
The metal foil treated in accordance with the present invention is any metal foil that may be laminated with a resin based material, such as an epoxy prepreg. The metal foil treated in accordance with the present invention is preferably an electrically conductive foil with copper and copper-based alloy foils being especially preferred. Other examples include aluminum, nickel, tin, silver, gold and alloys thereof. The metal foils are made in any suitable manner. Typically, the metal foils are made using one of two techniques. Wrought or rolled metal foil, such as copper foil, is produced by mechanically reducing the thickness of a metal or metal alloy strip or ingot by a process such as rolling. Electrodeposited foil is produced by electrolytically depositing metal ions, such as copper ions, on a rotating cathode drum and then peeling the deposited strip from the cathode. Electrodeposited copper foils are especially preferred.
The metal foils typically have nominal thicknesses ranging from about 0.0002 inch to about 0.2 inch. Metal foil thickness is sometimes expressed in terms weight and typically the foils of the present invention have weights or thicknesses ranging from, for example, about ⅛ to about 14 oz/ft
2
. Especially useful metal foils are those having weights of ½, 1 or 2 oz/ft
2
, and in particular, copper foil having weights of ½, 1 or 2 oz/ft
2
.
Electrodeposited metal foils have a smooth or shiny (drum) side and a rough or matte (metal deposit growth front) side. The side or sides of the metal foil (electrodeposited or wrought) which may be contacted with an inert silane, titanate or zirconate in accordance with the invention can be the rough or matte side, shiny side, or both sides (standard treated foil, reverse treated foil and double treated foil). Standard treated metal foil has its matte side treated, reverse treated metal foil has its shiny side treated, and double treated metal foil has both matte and shiny sides treated.
The sides may be a “standard-profile surface,” “low-profile surface” or “very-low-profile surface.” Especially preferred embodiments involve the use of foils with matte surfaces and st
Centanni Michael A.
Poutasse Charles A.
Aftergut Jeff H.
Gould Electronics Inc.
Renner , Otto, Boisselle & Sklar, LLP
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