Effect of Ni-Cr seed layer thickness on the adhesion characteristics of flexible copper clad laminates fabricated using a roll-to-roll process

The adhesion strength of a Cu/Ni-Cr/polyimide flexible copper clad laminate (FCCL), which was manufactured via a roll-to-roll process, was evaluated according to the thickness of the Ni-Cr seed layer using a 90° peel test. The changes in the morphology, chemical bonding, and adhesion properties were characterized using a scanning electron microscopy (SEM), an atomic force microscopy (AFM), and an X-ray photoelectron spectroscopy (XPS). The thickness of the Ni-Cr (Ni:Cr = 80:20) seed layer in which the maximum peel strength of the FCCL was observed was 200Å. The higher FCCL peel strength was attributed to the lower proportion of C-N bonds and higher proportion of C-O and carbonyl (C = O) bonds in the polyimide surface compared with the FCCL with a lower adhesion strength. The FCCL with a higher peel strength had a fractured polyimide surface with a higher surface roughness. The adhesion strength between the metal and polyimide was pirmarily attributed to the chemical interaction between the metal layer and the functional groups of the polyimide.