Stock material or miscellaneous articles – All metal or with adjacent metals – Foil or filament smaller than 6 mils
Reexamination Certificate
2001-04-12
2003-02-25
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Foil or filament smaller than 6 mils
C428S658000, C428S674000, C428S632000, C428S626000, C428S935000, C205S177000, C205S244000
Reexamination Certificate
active
06524723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to copper foil for printed circuit boards. More specifically, this invention concerns the copper foil for printed circuit boards—the copper foil having a surface so treated as to be provided with a uniform rough condition and a high adhesion to resins for use in the semiconductor field represented by printed circuit boards.
2. Description of the Prior Art
Printed circuit boards have been used as electronics and electric materials in large quantities and improved in performance and reliability, and the properties required in the printed circuit boards are getting complicated and diversified. The copper foil, one of the constituent materials of the printed circuit board, too, has to meet high quality requirements.
Printed circuit boards are made in the following process. First, the matte side of copper foil is put on or laminated with an insulating resin-impregnated base material, heated and press-bonded into a copper-clad laminate. Then a wiring circuit is formed to obtain a printed circuit board.
The glass-epoxy resin (grade FR-4) which is widely used as resin-impregnated base material is pressed for 1 to 2 hours at about 170° C. into a copper-clad laminate. Some high heat-resistant resins such as glass-polyimide resin requires pressing for two hours at a higher temperature, that is, 220° C.
As copper foil for printed circuit boards, the electro- deposited copper foil with a matte surface on one side and a shiny surface on the other side is predominately used. An untreated electro-deposited copper foil called crude foil is made by depositing copper by electrolysis and then subjecting it to the following surface treatment.
That is, the side of copper foil for printed circuit boards—the side that is bonded to the resin base material—is treated to secure an adequate peel strength this way. In the case of electro-deposited copper foil, the side (non-shiny side) to be bonded to the base material (and in the case of rolled copper foil, either of the sides) is pickled and roughened, and in addition, is given such treatments as to secure heat discoloration resistance, chemical resistance and such treatments as to improve and stablize etching properties. On the other hand, the side not to be bonded to the resin base material requires properties different from those on the other side—heat discoloration resistance and solder-ability.
Therefore, the bonding side and the non-bonding side of copper foil for printed circuit boards require different treatments, and a variety of techniques have been developed and proposed, which have made available copper foils for printed circuit boards with high functional surfaces.
For improvement of dimensional accuracy, furthermore, some copper foils for printed circuit boards are subjected to a long post-curing at a high temperature after pressing, and the needs of copper foils for printed circuit boards requiring heat discoloration resistance are increasing year by year. In addition, flexible printed circuit boards using other than the glass-epoxy resin base material are often subjected to heat treatment for a long time at a high temperature. Now, the heat discoloration resistance is one of the most important properties required on the non-bonding side of the copper foil.
Furthermore, multi-layer printed circuit boards are made in the following procedure. A wiring circuit is formed on the copper foil on a base material like glass-epoxy resin to obtain a primary laminate. On the circuit of this primary laminate, another resin board is laminated into a multi-layer printed circuit board.
The wiring circuit formed on the primary laminate is given a black oxide treatment to improve the adhesion as pretreatment before another resin base material is laminated thereon. In some cases, before a black oxide treated layer is formed, the wiring circuit is soft-etched in order to improve the adhesion between the wiring circuit and the black oxide treated layer.
Or, in some cases, copper foils are soft-etched before the formation of a circuit to increase the adhesion of the etching resist which is used to form a wiring circuit.
As mentioned above, the soft etching step is indispensable in making a printed circuit board. It is required that the treated surface is large in unevenness and has a uniform rough condition.
As soft etching agents, the following chemicals are generally used: sodium peroxodisulfate—sulfuric acid, ammonium peroxodisulfate—sulfuric acid, hydrogen peroxide—sulfuric acid.
A number of different techniques for maintaining the heat discoloration resistance have been proposed.
For example, Japanese publicized examined patent application gazette No. 54-29187 discloses a process involving forming a coat by dipping copper in an alkaline aqueous solution containing zinc or applying current with copper as cathode in the same solution. Japanese publicized examined patent application gazette No. 58-7077 discloses a process of providing a coated layer formed of zinc or zinc oxide and an oxide of chromium. Japanese publicized examined patent application gazette No. 2517503 discloses a process of chromating after forming a Zn—Ni alloy layer. Japanese unexamined patent application gazette No. 5-299834 proposes a copper foil provided with a composite layer containing zinc, chromium and phosphorus.
By any of those soft etching techniques, however, it is impossible to obtain a copper foil surface with much unevenness and a uniform rough condition. The subsequent black oxide treatment, too, fails to provide sufficient adhesion. Thus, no processes that can improve soft etching property enough have been proposed.
In addition, the coated layer of a mixture made of zinc or zinc oxide and an oxide of chromium disclosed in Japanese publicized examined patent application gazette No. 58-7077 is satisfactory in solder-ability but the problem is that the coated layer is so thin that the heat discoloration resistance and rust-prevention are poor. Also, the copper foil surface obtained according to the process of chromating after formation of a Zn—Ni alloy layer disclosed in Japanese patent No. 2517503 has a problem with solder-ability.
SUMMARY OF THE INVENTION
It is accordingly an object of this invention to provide a copper foil for printed circuit boards, especially with excellent soft etching property, heat discoloration resistance, rust-proofing, solder-ability etc. and a process of treating the surface.
The foregoing object is effected by the invention as will be apparent from the following description. That is, a first layer is formed by applying 12 to 50 mg/m
2
of a sulfur-contained zinc alloy containing 0.1 to 2.5 percent by weight of sulfur on the surface on at least one side. And then a second layer or a chromate layer is formed on the first layer.
This arrangement provides a copper foil for printed circuit boards excellent especially in soft etching property, heat discoloration resistance, rust-proofing, solder-ability etc.
In other words, the sulfur-contained zinc alloy layer has much to do with soft etching property. The presence of sulfur promotes the roughening effect of the soft etching solution on the surface of copper foil and improves the soft etching property. Furthermore, since the film formed of the sulfur-contained zinc alloy layer alone is poor in rust-prevention and heat discoloration resistance, the chromate layer is formed to improve the rust-prevention and heat discoloration resistance.
The above-mentioned second layer is a chromate layer formed by applying 0.5 to 2.5 mg/m
2
of chromium and 1.5 to 6 mg/m
2
of phosphorus.
According to this arrangement, the chromate layer is made to contain phosphorus to bring the quantity applied on the copper foil to a specific level, which further improves rust-prevention and heat discoloration resistance.
First, the first layer of the copper foil for printed circuit boards is explained. The first layer is formed by depositing a zinc layer containing sulfur on the shiny side of the copper foil.
It is required that the first layer
Hirose Masaru
Takami Masasto
Fukuda Metal Foil & Powder Co., Ltd.
Greigg Ronald E.
Zimmerman John J.
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