Profile-Free Copper Foil for High-Density Packaging Substrates and High-Frequency Applications

A new profile-free copper foil has been developed whose surface roughness is Rz <1.5 mum with satisfactory adhesion strength. An original surface treatment provided affords good peel strength (0.7 kN/m or more) equivalent to that for the conventional roughened foil with sufficient reliability. With the new profile-free copper foil, the conventional subtractive method is applicable to the wiring of 60 mum pitch or less, and the short-circuit fault of electroless Ni/Pd/Au plating that is prone to occur in fine wiring could be restrained since the wiring is formed on a smooth surface. Moreover, the transmission loss at 5 GHz band is decreased by 8 dB/m since the surface roughness of the conductor line is suppressed