PREPARATION AND CHARACTERIZATION OF Ni-Zn FERRITE THIN FILMS ON COPPER FOILS FOR PCB

摘要

The present article describes the deposition of Ni-Zn ferrite thin films and Ni-Zn ferrite/ silicon oxide-multilayers on copper foils for printed circuit boards (PCB). Ni-Zn ferrite was deposited by de-magnetron sputtering and silicon oxide was deposited by rf-magnetron sputtering in the same sputtering system LA 440 S. The substrates are electro-chemically produced copper foils. The copper foils are cleaned by rf-etching in an Ar-plasma before the deposition. The layer thickness of the Ni-Zn ferrite films amounts between 1000 nm and 4000 nm. The layer thickness of the multilayers amounts between 300 nm and 2000 nm. The multilayers consist of 4 Ni-Zn-ferrite layers and 4 silicon oxide layers. The structure, texture and residual stresses of the films were investigated by x-ray diffraction (XRD) measurements. The chemical composition was determined by x-ray fluorescence and EDX. The diffraction patterns indicates the development of the spinel ferrite structure. The Ni-Zn ferrite thin films are polycrystalline and show no or a weak texture. The surface morphology was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The grain size of the Ni-Zn ferrite crystals increases with increasing layer thickness. Very special attention was turn towards the adhesive strength of the layers. The adhesive strength is very important for the further processing of the deposited layers on copper foils to PCB. The adhesive strength of the layers was investigated by bending tests, deep drawing tests and squeezing tests. A direct determination of the adhesive strength was not possible. The mechanical strain applied in these tests is comparable to this at the PBC production. The investigations show a very high adhesive strength of the deposited layers on the copper foils.