Sodium Hypophosphite In Electroless Copper Plating Process - (dimethylamino) Borane Reduction System

In recent years, with more and more serious environmental pollution problems, the electroless copper plating technology turned to the environment-friendly directions. The electroless copper plating system with sodium hypophosphite as the reducing agent has been received people's attention. But because of the poor catalytic ability of the copper deposisted, the nickel ions was added to the electroless plating bath, which caused a bad copper film obtained from the electroless plating bath, showing the wine color and the higher resistance. It is bad for the applications.In order to improve the poor copper film quality, reduce the nickel content of the copper deposits film, HEDTA (Hydroxyethyl ethylenediamine triacetic acid) and Na2EDTA (Ethylenediamine tetraacetic acid disodium salt) was used as the complexing agent of the electroless copper plating solution using sodium hypophosphite. For the approximate stability of [CuEDTA]2+ and [NiEDTA]2+, the copper ions deposited easily compared with nickel ions, which may induced a pure copper deposits film obtained from the bath. On the other hand, the electroless copper plating did not always continue with the prolonged time because of the high stability of the [CuEDTA]2- and [NiEDTA]2- and the poor catalytic ability of the copper film, So DMAB (Borane dimethylamine complex) was added to enhance the reduce ability of the sodium hypophosphite.In this study, HEDTA was used as the complexing agent. By study the effect of the composition of the solution, temperature, pH and the experiment condition on the stability and the deposition rate of electroless copper plating bath, we confirmed the composition of the solution:CuSO4-5H2O 0.04 mol L-1, NiSO4·6H2O 0.0033 mol L-1, HEDTA 0.06 mol L-1, NaH2PO2·H2O,0.32 mol L-1, H3BO3 0.48 mol L-1, The operating temperature was 80℃and the pH was 9.0. The result of the research indicated that the basic solution showed the good stability。But because the high stability of the [CuEDTA]2- and [NiEDTA]2-, the experiment process could not be repeated successfully.With the help of the former research, Na2EDTA was used as another complexing agent with the approximative complexing ability of the HEDTA, But for the same reason of the high stability of [CuEDTA]2- and [NiEDTA]2-, the process could not be repeated successfully, so DMAB was added to the bath to enhance the reduce ability of the sodium hypophosphite, the basic composition of the solution was followed:CuSO4-5H2O 0.04 mol L-1, NiSO4·6H2O 0.0068 mol L-1, Na2EDTA 0.06 mol L-1, NaH2PO2·H2O,0.32 mol L-1, DMAB 0.008 mol L-1,The operating temperature was 80℃and the pH was 9.0. The result indicated that the solution showed a good stability and the deposition rate could reach to 1.1μm/h. A good copper deposited film was obtained with the better crystal appearance and lower nickel content (0.5%) via AAS analysis. The electronic chemistry result showed the limited addition of DMAB could accelerate the initial process, but did not effectively enhance the reduce ability of the sodium hypophosphite.The effect of the addition of thiourea and potassium ferrocyanide on the electroless copper plating was studied, the result indicated thiourea with the concentration of 0-1.5 ppm could improve the deposition rate, and it reached to 1.18μm/h with the concentration of 1.5 ppm, the color of copper film turned to be pink-copper. The AFM results showed Ra reached to the minimum of 218 nm with the concentration of 1.0 ppm, The XRD results indicated diffracted intensity of (111) crystal plane was strengthened, and the FWHM (term Full-Width Half-Maximum) reached to 0.462 and the crystallite size was15.8 nm with the concentration of 0.5ppm.The electronic chemistry result showed the acceleration effect of thiourea was owned to the increase of the mix current. On the other hand, the deposition rate reached to 1.22μm/h with the potassium ferrocyanide concentration of 1.0 ppm, the AFM results showed Ra reached to the minimum of 345 nm with the ferrocyanide concentration of 1.5 ppm, The XRD results indicated diffracted intensity of (111) crystal plane was strengthened, and the FWHM (term Full-Width Half-Maximum) reached to 0.658 and the crystallite size was 12.8 nm with the concentration of 1.0 ppm. The electronic chemistry result showed the addition of potassium ferrocyanide (2.0ppm) could decrease of the mix current which was bad for the copper deposition.By the sudy, we explored a new environmentally friendly electroless copper plating bath with a high stability. The copper deposited film had a good crystalloid and lower resistivity. It is very different from the former deposisted copper film with relative higher nickel content and a weaker quality. This is beneficial to the future study of electroless copper plating using sodium hypophosphite as the reducing agent.