Method of producing a surface-treated copper foil

#The present invention relates to a surface-treated copper foil which has been subjected to anti-corrosion treatment; to a method of producing the surface-treated copper foil; and to a copper-clad laminate employing the surface-treated copper foil.

#Conventionally, surface-treated copper foil has been employed as a material for producing printed wiring boards, which are widely used in the electric and electronics industries. In general, surface-treated copper foil is bonded, through hot-pressing, onto an electrically insulating polymer material substrate such as a glass-epoxy substrate, a phenolic polymer substrate, or polyimide, to thereby form a copper-clad laminate, and the thus-prepared laminate is used for producing printed wiring boards.

#Particularly, copper foil in which a zinc-copper (brass) plating layer, serving as an anti-corrosion layer, is formed on a surface of the foil (hereinafter such copper foil is referred to as “brass-plated anti-corrosive foil”) has been widely employed and exhibits excellent heat resistance characteristics (generally called UL heat resistance) during the manufacture of printed wiring boards. However, it has also been pointed out that brass-plated anti-corrosive copper foil has drawbacks such as low resistance to chemicals, particularly to hydrochloric acid. The resistance to hydrochloric acid can be evaluated through the following procedure. In practice, a printed wiring board having a pattern obtained from copper foil is immersed for a predetermined time in a hydrochloric acid solution of predetermined concentration. Instead of measuring the amount of the hydrochloric acid solution which has soaked into an interface between the copper foil pattern and the substrate of the wiring board, the peel strength before immersion and after immersion are measured. The percent loss in peel strength with respect to the initial peel strength is calculated, and the value is employed as an index of resistance to hydrochloric acid.

#Each of FIGS. 1(a) and 1(b) is a schematic cross-sectional view showing the layer structure of surface-treated copper foil.

#Each of FIGS. 2 and 3 is a general schematic cross-sectional view showing the constitution of baths included in a surface-treating apparatus for producing the surface-treated copper foil.

#The present inventors have attempted to provide surface-treated copper foil capable of consistently attaining a resistance against hydrochloric acid in percent loss of 10% or less as measured on a copper pattern prepared from the copper foil and having a line width of 0.2 mm, by bringing out the maximum effect of the silane coupling agent employed in brass-plated anti-corrosive copper foil. Also, the inventors have attempted to impart excellent moisture resistance to the surface-treated copper foil. Thus, the inventors have conducted extensive studies, and have found three important factors—i.e., the conditions of the anti-corrosion layer before the copper foil is treated with a coupling agent, which is the most important factor; the timing of treatment with the silane coupling agent; and drying conditions after treatment with the silane coupling agent—that must be addressed in order to bring out the maximum effect of the employed silane coupling agent. The present invention has been accomplished on the basis of these findings.

#In the present invention, there is provided a surface-treated copper foil for producing printed wiring boards which has been subjected to nodular treatment and anti-corrosion treatment of a surface of a copper foil, wherein the anti-corrosion treatment comprises forming a zinc-copper (brass) plating layer on a surface of the copper foil; forming an electrodeposited chromate layer on the zinc-copper (brass) plating layer; forming a silane-coupling-agent-adsorbed layer on the electrodeposited chromate layer; and drying the copper foil for 2-6 seconds such that the copper foil reaches 105° C.-200° C.

#In the present invention, there is provided a surface-treated copper foil for producing printed wiring boards which has been subjected to nodular treatment and anti-corrosion treatment of a surface of a copper foil, wherein the nodular treatment comprises depositing copper microparticles on a surface of the copper foil; seal plating so as to prevent release of the copper microparticles; and further depositing copper ultra-microparticles; and the anti-corrosion treatment comprises forming a zinc-copper (brass) plating layer on a surface of the copper foil; forming an electrodeposited chromate layer on the zinc-copper (brass) plating layer; forming a silane-coupling-agent-adsorbed layer on the electrodeposited chromate layer; and drying the copper foil for 2-6 seconds such that the copper foil reaches a temperature of 105° C.-200° C.