Surface treatment for a wrought copper foil for use on a flexible printed circuit board (FPCB)

Abstract

A surface treatment for a wrought copper foil relatives to a surface treatment procedure for a wrought cooper foil for use on a flexible PCB. The surface treatment comprises the steps of bi-polar electrochemical degreasing, acid etching and nodularization, electroplating a barrier layer and an anti-tarnish layer and coating a silane coupling agent layer to a copper foil. One side of the copper foil is nodularization, and a Zn—Ni barrier layer and a Cr—Zn anti-tarnish layer are electroplated on the copper foil. Finally, the organic silane coupling agent is coated to the roughened surface of the copper foil to modify the surface characters to impart the peel strength. Whereby, the cooper foil has very low profile, high peel strength, finer-pattern property, low HCl undercut and high thermal oxidation property.

What is claimed is:  
     
         1 . A surface treatment procedure of a copper foil for use on a flexible PCB comprising the following sequential acts: 
 electrochemically degreasing a copper foil;    acid etching the copper foil;    nodularization the roughened side of the copper foil in two stages of different current density;    electroplating a barrier layer on the copper foil;    electroplating an anti-tarnish layer on the copper foil; and    coating an silane coupling agent on the roughened surface of the copper foil;    wherein the electrochemically degreasing and acid etching processes are carried out by bi-polar electrochemical processes.    
     
     
         2 . The surface treatment of a copper foil as claimed in  claim 1 , wherein the bi-polar electrochemical degreasing process is performed in a solution of a base degreasing agent with a current density of 1˜5 A/dm 2  at 50˜80° C. for 10˜40 sec.  
     
     
         3 . The surface treatment of a copper foil as claimed in  claim 1 , wherein the bi-polar acid etching process is performed in a solution of 30˜90 g/L sulfuric acid with a current density of 2˜10 A/dm 2  at 30˜60° C. for 5˜20 sec.  
     
     
         4 . The surface treatment of a copper foil as claimed in  claim 1 , wherein the nodularization process is performed in two stages where: 
 a first stage is performed just after the copper foil enters a solution of copper ions in a 5-20 g/L plating agent and 50˜150 g/L sulfuric acid and an additive to the plating agent containing As +5 , As +3 , Ni +2 , W +6 , NO 3   − , Co +2  with a current density of 60˜150 A/dm 2  at 20˜40° C. for 1˜3 sec; and    a second stage just after the copper foil enters a solution the same as that in the first stage with a current density of 10˜60 A/dm 2  at 20˜40° C. for 4˜10 sec.    
     
     
         5 . The surface treatment of a copper foil as claimed in  claim 4 , wherein the additive in the nodularization process contains 0.5˜1.5 g/L of As +5 .  
     
     
         6 . The surface treatment of a copper foil as claimed in  claim 1 , wherein the barrier layer plating process is preformed in a Zn—Ni type boric acid solution with a 20˜100 g/L concentration of boric acid, 50˜300 ppm of an additive selected from saccharine or benzyl tri-ethyl ammonium bromide, a 0.5˜5.0 g/L concentration of Zn, a 0.25˜2.0 g/L concentration of Ni with a current density of 0.25˜2.0 A/dm 2  30˜60° C. for 2˜10 sec and pH in the range of 4.0˜6.0.  
     
     
         7 . The surface treatment of a copper foil as claimed in  claim 1 , wherein the anti-tarnish layer coating process is performed in a Cr—Zn type solution with a 2˜20 g/L concentration of sodium sulfate, a 0.2˜2.0 g/L concentration of Zn and a 0.5˜5.0 g/L concentration of chromic acid at 30˜60° C. with a current density of 0.5˜5.0 A/dm 2  for 2˜10 sec.  
     
     
         8 . The surface treatment of a copper foil as claimed in  claim 1 , wherein the organic silane layer spraying process is performed in a 3-glycidoxypropyl trimethoxy silane solution to coat the silane coupling agent on the roughened side of the copper foil.  
     
     
         9 . The surface treatment of a copper foil as claimed in  claim 8 , wherein the concentration of the 3-glycidoxypropyl trimethoxy silane solution is 0.2˜2.0%.