Effect of electrodeposited Cu interlayer thickness on characterizations and adhesion force of Ni/Cu/Ni coatings on polyetherimide composite substrates

Polyetherimide (PEI) composite is an engineering plastic with excellent performance. After metallization, the metalized PEI composite has some unique properties, such as electromagnetic shielding and high electrical conductivity. In this study, a composite coating of Ni/Cu/Ni was produced on the surface of a PEI composite substrate. Nickel and copper layers were plated by electroless and electrodeposition, respectively. The influences of copper interlayer thickness and heat treatment on the adhesion state of the multilayer coatings on the substrate were studied. The morphology and phase of the composite coatings were determined by optical microscopy, scanning electronic microscopy and X-ray diffraction, respectively. The surface roughness and contact angles of the samples before and after sandblasting were measured by surface profile-meter and goniometer, respectively. The electrical resistivity and adhesion state of the composite coatings were determined by multimeter and the tape test, respectively. The results show that Ni/7.54 μm Cu/Ni and Ni/58.6 μm Cu/Ni multilayer deposits were produced on the substrates. The top surface of the coating with a thin 7.54 μm-Cu interlayer was much rougher than that of a coating with a thick 58.6 μm-Cu interlayer. The initial alkaline electroless nickel layer with 5.8 ± 0.5% phosphorus was composed of a mixture of amorphous and nanocrystalline phases. The Cu interlayer consisted of a face-centered cubic crystalline structure. The phosphorus contents of the top nickel layers for samples #1 and #2 were composed of 6.53 ± 0.4 wt% and 3.52 ± 0.21 wt%, respectively. An increase in Cu interlayer thickness for the composite coating resulted in an increase in electrical resistivity. The average microhardness values of Ni/7.54 μm Cu/Ni PEI composite and the Ni/58.6 μm Cu/Ni PEI composite were about 300 HV0.1 and 244.2 HV0.1, respectively. The adhesion state of the Ni/7.54 μm Cu/Ni and Ni/58.6 μm Cu/Ni PEI composites could be classified as grade 5B and 3B, respectively. The adhesion force of the Ni/58.6 μm Cu/Ni multilayer on the substrate can be improved by heat treatment at 200 °C for 4 h.