High Acid And Low Copper System Plating Copper Microporous Super Filling And Micro-corrosion Analysis

Void-free and seamless filling is becoming the key problem in the fabrication of PCB wiring. The copper plating solution with the low copper (II) concentration and high sulfuric concentration has more advantages, such as, higher dispersion and coverage, however, the copper concentration was relatively low which made it more difficult for the filling performance of via-hole. Commissioned by a Hong Kong company, we carried out the research of bottom-up filling for via holes with low copper (II) concentration and high sulfuric concentration solution.The effects of the bottom-up filling with low copper(Ⅱ) concentration and high sulfuric concentration on microviafilling under direct current (DC) and periodical reverse current(PR) were studied. The results indicated that synergistic coordination existed between PEG, SPS and Cl- under DC to some extent, but the via-hole was not completely filled. The inhibitor PVP have severe inhibition on micro-via-filling, so four additives, namely, SPS, PEG, PVP and Cl" were investigated in the bottom-up filling, orthogonal experiments was designed, the concentration effect of each additive on the bottom-up filling was studied, after orthogonal experiments were optimized, the perfect filling was still not achieved.In addition, L25(35) orthogonal experimental design was used to evaluate the ability of copper filling. Through experiments, the electroplated copper was smooth and bright under the pulse parameters that the forward pulse duration (TF), and reverse pulse duration (TR),forward pulse current (Javg.a), reverse pulse current (Javg.a), and pulse frequency were 3 ms,1 ms,1 A/dm2,0.375 A/dm2 and 250 Hz respectively. The additives concentrations, namely, SPS, PEG were 2 ppm,60 ppm and 80 ppm respectively, bottom-up filling achieved. However, the ratio of via-hole filling was very low.Another investigation was the analysis of the composition for the MnO2-H2SO4 and MnO2-H2SO4-H3PO4 etching solution, UV-Vis and Raman spectrometer were used to the qualitative analysis of the etching solution. The results indicated that Mn(IV), Mn(III) and colloidal MnO2 were existed in MnO2-H2SO4 and MnO2-H2SO4-H3PO4. Also, the concentration of high state manganese concentration was roughly confirmed by titration, the high state manganese concentration in MnO2-H2SO4-H3PO4 was about ten times higher than MnO2-H2SO4. The relation of potential and etching effect was studied by electrochemical method. The results indicated that when the high state manganese concentration was higher, it was easier to get better etching effect during shorter time and lower temperature, and the etching efficiency was raised, otherwise, the etching efficiency was low. On the other hand, the redox potential should never be too high nor too low, when the redox potential was 1.426 eV, the etching effect was the best in MnO2-H2SO4, and the etching effect was relatively better when the redox potential was 1.34 eV in MnO2-H2SO4-H3PO4, under such redox potential, the difference of etching rate upon three phrase of ABS was bigger, more micro pores or cavities appeared, and the etching result was better. The relationship between redox potential and etching effect was studied by electrochemical station. The results indicated that when the high state manganese concentration was higher, it was easier to get better etching effect during shorter time and lower temperature, and the etching efficiency was raised, otherwise, the etching efficiency was low. On the other hand, the redox potential should never be too high nor too low, when the redox potential was 1.426 eV, the etching effect was the best in MnO2-H2SO4, and the etching effect was relatively better when the redox potential was 1.34 eV in MnO2-H2SO4-H3PO4, under such redox potential, the difference of etching rate upon three phrase of ABS was bigger, more micro pores or cavities appeared, and the etching result was better. At last, Atom Absorption Spectrometer was used to determine the total manganese concentration. It was suggested that Mn(IV) was not the only form in the etching solution, low state manganese like Mn(II), Mn(III) were also existed in the etching solution.