Copper metallization on polyimide films was carried out via a wet chemical process. This process included the chemical reaction of KOH with PI to form poly(amic acid) (PAA), ion exchange of doped K(+) with Cu(2+) to form Cu(2+)-doped PAA, doped Cu(2+) reduction by aqueous dimethylamine borane (DMAB) to form copper nanoparticles (CNPs) on PAA, and electroless copper (ELC) deposition catalyzed by CNPs on PAA. An organic additive, namely, bis(3-sulfopropyl)-disulfide (SPS), that can effectively reduce the size of CNPs and significantly enhance the chemical activity of CNPs for ELC deposition was used in this work. For comparison, doped Cu(2+) ions in the PAA were also reduced by hydrogen gas at 350 degrees C. The results show that only aqueous reductants can induce the reduced copper atoms to aggregate on the PAA surface and to form a granular copper layer that acts as a catalyst for the ELC deposition. Mechanisms for the aggregation of copper atoms and for activity enhancement of the CNPs due to SPS addition in the DMAB solution are proposed according to the evidence obtained from Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectrometry (XPS), field emission scanning electron microscopy (FESEM), cross-sectional transmission electron microscopy (TEM), and atomic force microscopy (AFM). The CNP-coated PAA films and the structures of the ELC deposits were characterized by X-ray diffraction (XRD) and UV-visible spectrophotometry (UV-Vis), respectively
Polyimide (PI) metallization using Ni-nanofilm (Ni-nF) as the copper barrier layer and catalyst layer of electroless copper deposition was carried out. The surface of the PI film was hydrolyzed by KOH to form a layer of poly-amic acid (PAA) and subsequently performed ion-exchange of K + ions with Ni 2+ ions. The doped Ni 2+ ions can be rapidly chemically reduced to the dense and continuous Ni-nF, if the reducing solution [i.e., dimethylamine borane (DMAB)] contained a trace amount of Ag + , Cu 2+ or Pd 2+ ions. To characterize the materials and propose a mechanism of Ni-nF formation, Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), and secondary ion mass spectrometer (SIMS) were employed in this work. The main reason of Ni-nF formation is caused by a high concentration gradient of doped Ni 2+ ions in the PAA that results from the addition of those metallic ions in the DMAB solution.
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