| The polycarbonates (PC), acrylonitrile-butadiene-styrene (ABS) and polyimide (PI) are the most commonly used three polymers because of their excellent properties, such as:electrical insulating property, shock resistance and a variety of decorative effects. They have been widely used in electric products, mechanical equipment and aerospace fields. With the surface metallization of PC, ABS and PI substrates, many specific properties of them can be enhanced and the range of application can be expanded. But without treatment, the surface of the substrates are very smooth, and the adhesion strength between the substrates and electroless plated copper films is generally weak because of the thermal mismatches. Therefore, surface modification processes are necessary to improve the adhesion strength and the surface hydrophily. In order to have a successful metallic deposition, a great number of methods have been introduced to enhance the surface roughness and the wettability of the substrate surface, such as wet chemical treatment, plasma processes, ion track etching and surface graft copolymerization treatments. Due to simplicity and low cost, the wet chemical treatment is one of the most frequently used processes for the metallization. The wet chemical treatment mainly includes four steps:degreasing, swelling, etching and neutralization treatments. Among them, the etching treatment is the key step. At present, the sulfo-chromic admixture is the most widely used etchant for PC, ABS substrates and PI films due to its high oxidative power at present, but the carcinogen Cr(VI) impose serious operating-problems. And so, the research about the low cost and environmentally friendly surface modification processes becomes more important.In this dissertation, a newly-designed swelling system was used to swell PC substrate before the etching treatment, the chromium-free and low environmental pollution chemical treatment was used for swelled PC and ABS substrates surface etching treatment, and the environmentally friendly photocatalytic treatment was used for ABS substrate and PI film surface modification treatment. After the substrates were treated properly by the above methods, the desired effects were obtained. The main works of the dissertation are as follows:1. PC is a macromolecule polymer which is a single-phase composition and contains many rigid groups being similar to the benzene ring. The dense structure prevents the etching agent from entering into it. And so, the swelling process is very necessary before the etching treatment. The mild swelling system containing N, N-dimethylformamide (DMF), ethanol and water was designed in the experiment. And the effects of DMF concentrations in the swelling solution on the surface etching performance were investigated after swelling and etching treatments at the fixed etching condition. The results of SEM observation indicated that the reaction points were exposed sufficiently after the PC substrate was swelled in proper concentration of DMF swelling solution. The exposed reaction points were beneficial for the etching treatment. The increase of DMF concentration could reduce the etching effect because PC substrate was excessively swelled. And so, the proper swelling condition was determined by the experiment.2. The H2SO4-MnO2-H2O ternary system was used for PC substrate etching after it was swelled properly, and the effects of H2SO4concentration, etching time, MnO2content and bath temperature on the surface physical and chemical properties and the adhesion strength between the substrate and electroless copper film were investigated. The redox potential of etching system and the soluble Mn(IV) ion concentration were measured by an electrochemical workstation and redox titration. The results indicated that redox potential of etching system increased with an increase of H2SO4concentration, and the oxidant capacity of the etching system increased correspondingly. Higher temperature could promote the etching reaction, but excessive temperature could cause over-reaction resulting in poor etching performance. It was found that the etching performance was excellent when the H2SO4concentration was12.3mol/L, the etching temperature and treatment time were70℃and20min, respectively. With the etching treatment, many cavities appeared on the PC surface and the density and depth of the cavities were large, the surface roughness reached the maximum value, and the PC surface changed from a hydrophobic to a hydrophilic. X-ray photoelectron spectroscopy (XPS) analysis further demonstrated that abundant hydrophilic groups were generated on the PC surface after the etching treatment, which was attributed that side chains in the PC resin were oxidized by the oxidant. The formation of hydrophilic groups strengthened the hydrophilicity of PC substrate. The maximum adhesion strength between the electroless plated copper film and PC substrate reached1.08kN/m, which was due to the higher surface roughness and strong surface hydrophilicity.3. In order to improve the etching performance, H3PO4was added into the MnO2-H2SO4-H2O ternary system to constitute a new quaternary system of MnO2-H2SO4-H3PO4-H2O. And so, effects of the H2SO4concentration, H3PO4concentration, treatment time and bath temperature upon the surface properties and the adhesion strength between the substrate and electroless copper film were investigated. The redox potential of etching system and the soluble Mn(IV) ion concentration were measured by an electrochemical workstation and redox titration. The results indicated that the Mn(IV)-H3PO4complex, as a strong oxidizing agent, could be formed with an addition of the H3PO4because of phosphoric acid strong coordination. And the soluble Mn(IV) concentration was enhanced to0.111mol/L, which is ten times larger than that in the ternary system (0.010mol/L). The etching process was a dynamic process, and the increase of the soluble Mn (IV) concentration was conducive to the supplement of the oxidant in etching process, increasing reaction rate, shortening treatment time and prolonging the useful life of the etching system. The results of SEM observation indicated that many dense uniform cavities appeared on the PC surface after the proper etching treatment, and the surface roughness increased significantly. Fourier trans-form-infrared spectroscopy (FT-IR) indicated that lots of hydrophilic groups were generated on the PC surface after the etching treatment. XPS analysis further demonstrated that side chains in the PC resin were oxidized by the oxidant, and some of the ester groups were cracked. The desired effect was achieved after the PC substrate was etched for a shorter period of time (10min) at lower temperature (60℃).4. The H2SO4-Na4P2O7-H2O-MnO2quaternary system was designed for ABS etching treatment. And effects of the H2SO4concentration and Na4P2O7content on the surface etching performance of ABS substrates were investigated. The redox potential of etching system and the soluble Mn(IV) ion concentration were measured by an electrochemical workstation and redox titration. The principle about ABS etching treatment is that the butadiene phase is oxidized selectively or preferentially by the oxidant in the etching system. The rate between the butadiene phase and the acrylonitrile and styrene phases is the largest when the oxidation capacity of system is in a proper range. After the etching treatment, the surface roughness reached to the maximum value, the surface hydrophilic property was strongest and the adhesion strength was largest. The results indicated that although the redox potential of etching system decreased with an addition of which is neutralization reaction of Na4P2O7with H2SO4, and results in a decrease of H+concentration in the etching system, the soluble Mn(IV) ion concentration increased to0.019mol/L, which is two times larger than that in the ternary system (0.010mol/L). The etching process was a dynamic process, and the increase of the soluble Mn(TV) ion concentration was conducive to the supplement of the oxidant in etching process, increasing redox reaction rate, shortening treatment time and obtaining a better etching effect. The redox potential could be in a proper range through increasing the H2SO4concentration when the Na4P2O7content was fixed. The adhesion strength between the electroless copper film and ABS substrate was measured by qualitative and quantitative determination. The results indicated that the desired etching effect could be obtained when the H2SO4concentration and the Na4P2O7content were12.9mol/L and58g/L, respectively. Many dense uniform cavities appeared on the ABS surface after the proper etching treatment, the average roughness (Ra) reached the maximum (155nm), and the surface contact angle decreased from92°to31°, indicating strong wettability. The maximum adhesion strength between the electroless copper film and ABS substrate reached1.30kN/m.5. In the photocatalytic treatment, the photo-generated holes react with water molecules and hydroxyl ions adsorbed on the surface of the photocatalyst (TiO2) to form hydroxyl radicals. The resulting hydroxyl radicals, as very strong oxidizing agents, could modify ABS surface. Effects of the TiO2content, irradiation time and UV power upon the surface characterization and the adhesion strength between ABS surface and electroless copper film were investigated. The results indicated that the hydrophilic of ABS substrate and the adhesion strength increased with an increase of the UV power and a prolongation of irradiation time. The adhesion strength first increased and then decreased with an increase of TiO2content, and it was the highest value when the TiO2content was1.0g/L, which was attributed to agglomeration of TiO2particles in the high content TiO2dispersed solution decreasing the oxidative capacity of·OH radicals. With the photocatalytic treatment, the surface topography and the surface roughness changed little, which was attributed that some butadiene phase on the surface were oxidized by the aggressive species such as hydroxyl radical. FT-IR indicated that lots of hydrophilic groups were generated on the ABS surface after the photocatalytic treatment, and the density of hydrophilic groups increased with an increase of UV power and irradiation time. XPS analysis further demonstrated that the density of polar groups formed on the ABS surface by the photocatalytic treatment was much higher than that etched by H2SO4-MnO2-H2O ternary system. The adhesion strength between the substrate and the electroless plating film reached1.25kN/m. The results indicated that the photocatalytic treatment was an environmentally friendly and effective method to replace commercial wet chemical process for the ABS surface modification. With the photocatalytic treatment, not only was the high adhesion strength obtained, but also the smooth ABS surface was kept.6. The combination of TiO2photocatalytic treatment and alkaline hydrolysis was used to modify polyimide (PI) film. And effects of the TiO2content, UV power and irradiation time upon the treatment performance were investigated. The results indicated that the surface topography of PI film had no obvious change before and after the photocatalytic treatment. The hydrophilicity of PI film and the adhesion strength between PI surface and electroless copper film increased with the increase of UV power and a prolongation of irradiation time, and did not increased linearly with an increase of TiO2content. FT-IR spectra that abundant hydrophilic groups were generated on the PI surface after the photocatalytic treatment, and the density of hydrophilic groups increased with an increase of UV power and irradiation time. XPS analysis further demonstrated that the PI films were cleaved and the amide groups and carboxyl groups were formed on the surface of the PI films after the photocatalytic treatment, and the-COOH group content reached6.1%. The surface hydrophilicity had been strengthened greatly by the formation of polar hydrophilic groups, and the adhesion strength was increased accordingly. After PI film was treated for30min by the1.0g/L TiO2suspension solution at300W, the maximum adhesion strength reached0.78kN/m. The results indicated that the photocatalytic treatment was an environmentally friendly and effective method for the PI films surface modification. |
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