Process and apparatus for the manufacture of high peel-strength copper foil useful in the manufacture of printed circuit boards, and laminates made with such foil

An electrolytic process for producing copper foil having a bond-enhancing treatment electrodeposited on a matte side of the foil, which process comprises:

• (a) providing a core foil by passing an electric current from a primary anode through a main electrolyte stream containing copper ions flowing in a first gap between a rotating drum cathode and the primary anode in a first electrodeposition zone under first mass transfer conditions, including a first current density, effective to electrodeposit on the cathode a core copper foil having a fine-grained microstructure and a matte side with a matte surface having micro-peaks and-valleys;
• (b) passing the core foil to a second electrodeposition zone having a secondary anode spaced from the matte surface of the core foil and passing the main electrolyte stream into a second gap between the secondary anode and the core foil;
• (c) flowing a stream of secondary electrolyte containing copper ions into the second gap between the secondary anode and the core foil to mix with the main electrolyte stream in the second gap and form a mixed electrolyte stream;
• (d) passing an electric current from the secondary anode through the mixed electrolyte stream to the core foil in the second electrodeposition zone under second mass transfer conditions, including a second current density greater than the first current density and at or near the limiting current density, which provide mass transfer conditions poorer than that in the first electrodeposition zone, and which are effective to electrodeposit on the matte surface of the core foil a first layer of copper having the form of elongated micro-projections extending outwardly from the matte surface;
• (e) passing the core foil having the first layer deposited thereon to a third electrodeposition zone having a tertiary anode spaced from the first layer on the core foil;
• (f) flowing the mixed electrolyte stream from the second electrodeposition zone into a third gap between the tertiary anode and the first layer and
• (g) passing an electric current through the mixed electrolyte stream from the tertiary anode to the core foil having the first layer deposited thereon under third mass transfer conditions, including a third current density less than the second current density, which provide a mass transfer better than that in the second electrodeposition zone, and which are effective to electrodeposit on the first layer a mechanically strong second layer of copper which encapsulates the first layer and conforms to the surface contours of the first layer.