Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonelectrolytic coating after depositing...
Reexamination Certificate
2001-04-12
2002-07-16
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonelectrolytic coating after depositing...
C205S197000, C205S215000, C205S219000
Reexamination Certificate
active
06419811
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the surface treatment of copper foil. More specifically, this invention concerns the method of treating the surface of copper foil to create a surface with a rough and uniform condition and with a high adhesion to resins for use in the field of printed circuit boards.
2. Description of the Prior Art
Copper foil is used in printed circuit boards for electronics and electric materials in large quantities.
Printed circuit boards are made in the following process. First, the matte side of copper foil is put on an insulating resin-impregnated base material, heated and press-bonded into a copper clad laminate. The glass-epoxy resin base material (FR-4) which is widely used is pressed at 170° C. for one to two hours. Some base materials like glass and high heat-resistant resins such as polyimide require pressing for two hours at 220° C.
Printed circuit boards have been 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 vigorous quality requirements.
Copper foil for printed circuit boards is available in two kinds, that is, rolled copper foil and electrodeposited copper foil. The electrodeposited copper foil which has a matte side and a shiny side is used in predominantly large quantities.
The electrodeposited copper foil is generally made in the following process. Copper is deposited from a copper electrolytic solution in an electrodeposition apparatus to obtain a crude foil which is called untreated copper foil. Then, the matte side (non-shiny side) of the untreated copper foil is pickled for roughening treatment to secure adhesion to the resin. Then, the copper foil is treated to improve and stabilize such properties as heat resistance and chemical resistance and etching properties.
A number of techniques for those treatments have been developed and proposed, which make available copper foils with high-functional surfaces.
Printed circuit boards have been highly densified in recent years, and the insulating layer or the resin layer is made very thin in thin printed circuit boards and build-up process printed circuit boards, for example. Such printed circuit boards can present problems with inner-layer insulating properties if the roughened side of copper foil is high in degree of roughness.
In a recent trend toward fine lining, furthermore, a matte side with a low profile is being expected, because a lower degree of roughness on the roughened side of copper foil can keep the inter-line insulation better. However, if the adhesion is not sufficient, the copper foil circuit will present such problems as peeling, lifting, and delamination in the course of or after manufacturing. Those requirements are conflicting with each other, and a process of surface treatment that meet those conflicting requirements is expected.
Furthermore, as base material for printed circuit boards, glass-epoxy resin base material (FR-4) has been widely used, while base materials impregnated with special resins like polyimide resin, high heat-resistant and low dielectric constant resins are finding increasing use in printed circuit boards because of the high reliability.
Such special resins are low in adhesion for copper foil. It is hoped that a process of surface treatment should be developed that solves the adhesion problem on the low profiled surface.
Meanwhile, the shiny side or the reverse side of the matte side of copper foil requires properties different from those on the matte side. They include resistance to heat color change, solder wettability and resist adhesion. The matte side needs a process of surface treatment different from that for the shiny side.
In the past, no solder wettability is required in the shiny side of copper foil for use in multi-layer printed circuit boards, especially as inner layer and did not need to be roughened.
But even in an application called DT (double treatment) foil other than copper foil, light roughening has come to be hoped for to improve the adhesion for resist and the adhesive strength in treatment of inner layers in forming a printed circuit board.
Sophisticated treatments have been developed to meet a variety of requirements made on the matte side and the shiny side of copper foil.
A number of processes of roughening copper foil are disclosed. For example, Japanese publicized examined patent application gazette No. 53-38700 discloses a process involving a three-step electrolytic treatment in an acid electrolytic bath containing arsenic. Japanese publicized examined patent application gazettes Nos. 53-39327 and 54-38053 disclose processes comprising carrying out electrolysis at around the limiting current density in an acid copper electrolytic bath containing arsenic, antimony, bismuth, selenium, and tellurium. Japanese patent No. 2717911 discloses a process involving electrolysis at around the limiting current density in an acid copper electrolytic bath containing either chromium or tungsten or both.
But some of the above-mentioned processes use such substances as arsenic, selenium and tellurium that are harmful to humans and have to be extremely limited in their uses in the light of the environmental protection. It is feared that the harmful components contained in copper foil could pollute the environment when printed circuit boards are recycled or disposed of as industrial waste.
One of the disclosed processes of surface treatment involves treatment in a bath containing chromium and tungsten. In this process, the roughened surface condition improves in uniformity but is low in adhesive strength to glass epoxy resin base material (FR-4) and especially glass-polyimide resin base material etc. and is not practically useful.
SUMMARY OF THE INVENTION
In view of the prior art described above, including the 20 disadvantages and problems of the prior art, it is an object of the present invention to provide an easy process of copper foil surface treatment which does not use such harmful substances as arsenic, selenium and tellurium and which produces a copper foil with a uniform matte condition, a low surface rougheness and a high adhesive strength for such base resins with a weak adhesion as polyimide resin.
The foregoing object is effected by the invention as will be apparent from the following description. That is, at least one side of copper foil is subjected to a roughening treatment involving a cathodic electrolysis near or above the limiting current density in an electrolytic bath containing titanium ions and tungsten ions and prepared by adding sulfuric acid and copper sulfate so as to have copper protrusions deposited and then the depositions are coated with copper or a copper alloy in a cathodic electrolysis. Then the surface of the above-mentioned copper or the copper alloy is given at least one of the following rust-proofing treatments—chromate treatment, organic rust-proofing treatment and silane coupling agent treatment.
It is preferable that the concentration of titanium ions is 0.03 to 5 10 g/l and the concentration of tungsten ions is 0.001 to 0.3 g/l in the electrolytic bath.
The roughening treatment method according to the present invention will be described. First, untreated copper foil is pickled to remove oxides and stains on the surface. Then, the matte surface of the copper foil is subjected to cathodic electrolysis near or above the limiting current density in an electrolytic bath so as to have copper protrusions deposited on the surface, thus forming an uneven surface.
The deposited copper protrusions are weak in adhesive strength to the surface of the copper foil. After that, therefore, a coat of copper or copper alloy is formed by cathodic electrolysis so as to coat the protrusions with the copper, thus keeping copper foil and copper protrusions from peeling off. Then, the coat of copper or copper alloy is subjected to rust proofing treatment.
The cathodic electrolysis co
Hirose Masaru
Manabe Hisanori
Takami Masasto
Fukuda Metal Foil & Powder Co., Ltd.
Greigg Ronald E.
Wong Edna
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