Effect of RF sputtering power on the adhesion of Ni thin film to polyimide

This study represents the results of an investigation of the peel strength and surface morphology according to the Ni sputtering power in producing Cu/Ni/PI structured flexible copper clad laminate (FCCL) using polyimide (PI). In order to analyze the surface morphologies of the sputtered Ni, Cu, and electrodeposited copper foil, and their crystal structure and interface binding structure, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used. The surface roughness of the deposited layers and the crystal structure of the electrodeposited Cu layers varied according to the Ni sputtering power. In the range of RF output of 100~400 W in the Ni deposition process, the metal layers deposited at a power of about 300 W showed a homogeneous surface morphology and also exhibited a high peel strength for polyimide. The peeling that occurred at the interface of NiPI in the specimen fabricated using an Ni sputtering power of 300 W was due to the fact that the peeling usually occurs inside the polyimide. In the results of the XPS analysis on the separated Ni surface, the peaks of C and N, which are the major elements in polyimide, showed higher levels compared to those observed under the other conditions.