Microetching and electroless nickel plating of fine lines on flexible printed circuit board
[Introduction]Chemical microetching is widely used as a pretreatment in different phases during manufacturing of printed circuit boards(PCB).[Method]The fine lines on flexible printed circuit boards(FPCB)were microetched respectively in different electrolytes i.e.sulfuric acid-sodium persulfate electrolyte(coded as SA-SP),sulfuric acid-hydrogen peroxide electrolyte(coded as SA-HP),and formic acid-copper chloride electrolyte(coded as FA-CC).The microetching degree,microetching rate,and surface roughness of fine line after being microetched were compared by laser spectroscopy confocal microscopy(LSCM).The surface morphologies of copper lines before and after being microetched with different electrolytes and the effects of different electrolytes on electroless nickel plating were studied by scanning electron microscopy(SEM).[Result]The microetching capacity of the three electrolytes was in the following descending order:SA-SP>SA-HP>FA-CC.The surface roughness of copper lines was increased with the extending of microetching time no matter which electrolyte was used.A small amount of cuprous chloride was formed on copper line surface after being microetched with the FA-CC electrolyte.The composition of microetching electrolyte had great effect on the electroless nickel plating of copper lines.The nickel coating electrolessly plated on the copper lines microetched with the SA-HP electrolyte was bright,but an excessive nickel plating phenomenon occurred.The excessive nickel plating on the copper lines was severe when microetching with the FA-CC electrolyte,but effectively controlled when microetching with the SA-SP electrolyte.However,the Ni coating plated electrolessly on the copper lines microetched in the SA-SP electrolyte was dark.[Conclusion]It is recommended adding brightening agent to the electroless nickel plating bath to increase the brightness of Ni coating.
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