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

Abstract

A one-step, integrated process and apparatus for producing electrolytic copper foil having a dual-layer copper bond-enhancing treatment electrodeposited on the matte side of the foil, which employs two “super anodes” on a rotating drum cathode to deposit the treatment.

What is claimed is:  
     
         1 . 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 prepared by passing an electric current from a primary anode through a main electrolyte containing copper ions to a cathode spaced from 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; and    (c) flowing a stream of secondary electrolyte containing copper ions into a gap between the secondary anode and the core foil under laminar flow conditions;    (d) passing an electric current from the secondary anode through the flowing secondary electrolyte 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 a mass transfer poorer than that in the first electrodeposition zone, and which are effective to electrodeposite 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 secondary electrolyte from the second electrodeposition zone into a gap between the tertiary anode and the first layer under laminar flow conditions; and    (g) passing an electric current through the flowing electrolyte 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.    
     
     
         2 . The process of  claim 1 , wherein the secondary anode is positioned adjacent a trailing end portion of the primary anode, the tertiary anode is positioned adjacent a trailing end portion of the secondary anode, the core foil is passed serially on the drum cathode to the second and third electrodeposition zones, the main electrolyte is passed serially from the first electrodeposition zone to the second and third electrodeposition zones, and the secondary electrolyte is injected into the main electrolyte at a point between the trailing end portion of the primary anode and a leading end portion of the secondary anode.  
     
     
         3 . A copper-clad laminate comprising a polymeric substrate and copper foil produced by the process of  claim 1 , wherein the matte side of the copper foil is bonded to the substrate through the first and the second layers.  
     
     
         4 . The copper foil of  claim 1 , further including a copper bond-enhancing treatment electrodeposited on a shiny side of the core foil opposite the matte side.  
     
     
         5 . A copper-clad laminate comprising a polymeric substrate and the copper foil of  claim 4 , wherein the shiny side of the foil is bonded to the substrate through the bond-enhancing treatment.  
     
     
         6 . The process of  claim 2 , wherein the main electrolyte and the secondary electrolyte is an aqueous solution containing from about 60 to 110 grams per liter of copper ions and from about 40-150 grams per liter of sulfuric acid, and the electrolyte is maintained at a temperature in the range of from about 100 ° F. to about 180° F.  
     
     
         7 . The process of  claim 2 , wherein the first current density is from about 20 to about 100 A/DCM 2 , the second current density is from about 500 to about 700 A/DCM 2 , and the third current density is from about 80 to about 120 A/DCM 2 .  
     
     
         8 . The process of  claim 6 , wherein the electrolytes further include one or more additional agents.  
     
     
         9 . A rotating drum cathode machine comprising a rotating drum cathode; a primary anode spaced from the cathode and extending around a portion of the cathode, the primary anode having a leading end portion and a trailing end portion, primary electrolyte supply means for circulating an electrolyte in a first gap between the cathode and the primary anode at a first velocity; first electric supply means for passing a direct electric current from the primary anode through the primary electrolyte to the cathode at a first current density, a secondary anode, having a leading end portion and a trailing end portion, spaced from the cathode and separated from but adjacent the trailing end portion of the primary anode; secondary electrolyte supply means for flowing secondary electrolyte in a second gap between the secondary anode and the cathode at a second velocity greater than the first velocity; second electric supply means for passing a direct electric current from the secondary anode to the cathode at a second current density greater than the first current density, a tertiary anode, having a leading end portion and a trailing end portion, separated from but adjacent the trailing end portion of the secondary anode and spaced from the cathode to provide a third gap between the cathode and the tertiary anode for receiving electrolyte flowing in the second gap; third electric supply means for passing a direct electric current from the tertiary anode to the cathode at a third current density less than the second current density, and electrolyte withdrawal means for withdrawing electrolyte from the third gap adjacent the trailing end portion of the tertiary anode.  
     
     
         10 . The rotating drum cathode machine of  claim 9  wherein the first current density is in the range of from about 20 to about 100 A/DCM 2 , the second current density is in the range of from about 500 to about 700 A/DCM 2 , and the third current density is in the range of from about 80 to about 120 ANDCM 2 .