Effect of Cr Thickness on Adhesion Strength of Cu/Cr/Polyimide Flexible Copper Clad Laminate Fabricated by Roll-to-Roll Process

The adhesion strength of a Cu/Cr/polyimide (PI) flexible copper clad laminate (FCCL), which was manufactured by the roll-to-roll process, was evaluated according to the thickness of the Cr seed layer using the 90° peel test. The changes in the morphology, chemical bonding and adhesion properties were characterized by scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The peel strength of the FCCL decreased with increasing Cr layer thickness. The higher FCCL peel strength was attributed to the lower proportion of C-N bonds and higher proportion of C-O or carbonyl (C=O) bonds on the PI surface compared to the FCCL with the lower adhesion strength. The FCCL with the higher peel strength had a fractured PI surface with a higher surface roughness. The adhesion strength between the metal and PI was mostly attributed to the chemical interaction between the metal layer and the functional groups of the PI.