Electrochemical Studies Of The Copper-Dimethylamine Borane System Chemical Deposition

At present, electroless plating copper has been used in the fields of aviation,electronic, machinery, car manufacturing, chemistry, petroleum, metallurgy, etc.However, the traditional formaldehyde chemical cu-plating process has been eliminatedfor the reasons of causing harm to human health and environment and high conditionrequirements. Therefore, it is extremely urgent to develop a new environmental friendlyelectroless copper process. Dimethylamineborane (DMAB), as a excellent reductant,has its unique advantages in the electroless copper process: mild reduction action, canbe used in various pH value, easily soluble in water and organic solvent; has highreducing capacity, and can produce good purity coating film, and performance. Hence,Cu-DMAB electroless copper process has become one of the new directions of thedevelopment of electroless plating copper. However, until now, there are few studies onthis area, so there exist the problems of confusing mechanism of the oxidation process,unidentified side reaction of the oxidation process and the influence of external factors,and even the mechanism consistent of the hydronoron and oxidation, etc. Given thesecircumstances, this paper will conduct a series of research focusing on this process.First, we have studied the stability of DMAB solution in different pH value. Afterthis research, we found out that DMAB will have hydrolysis reaction in the lower pHvalue, and will comparatively slow hydrolysis reaction with no influence on theresearch of electrochemistry in higher pH value. At the same time, we have tested theoxidizing reaction of DMAB on the electrode surface of gold, platinum, glassy carbon,and copper, with the results showing that different electrode will have different catalysisof its oxidizing process, glass carbon has the near none catalysis, and gold has the bestcatalysis. Hydronoron and DMAB both have a complicated, multistep oxidizingmechanism, but the differences are DMAB is an oxidizing reaction with6electrons,while hydronoron with8electrons. During the oxidizing process, both of them aregreatly affected by adsorption, but DMAB is more obvious. Even though we haveapplied many technical means on the study of the mechanism of DMAB, there are still alot of unknowns. However, according to the research results, we can tell that the two3-electron mechanism of the oxidizing process is a better fit for its characteristic.Second, we have further studied the oxidizing process of DMAB with theelectrode surface effect of three kinds of single crystal gold which are Au (111), Au (110), and Au (100); and we also studied the different intermediates in the oxidizingprocess using the infrared spectra technology. We found out that: first separation step ofDMAB’s oxidizing process is a simple chemical step, which not only influenced by thecatalysis of metal electrode surface, but also affected by the application potential; thecorresponding two3-electron transfer process of the two oxidation waves has matchedthe result of research on oxidizing mechanism in a high alkaline environment; thesuspected adsorption which found out in the previous research is real which means themutual effect between the electron surface and the reductant has great influence on theoxidizing process of DMAB; the intermediates might be BO2-or B4O7-during theoxidizing reaction conducted by the infrared spectra technology.Third, we have studied the current-voltage behavior of the complex, Cu (II), inwhich the1,5,8,12-tetraazadodecane were acting as complexing agent, and found outthat it was influence greatly by the pH value and electron surface. Under the conditionof strong alkaline, we found out that the electrochemical behavior of the coppercomplex on the glassy carbon surface is complicated. Its reduction was completed by areversible2-electron, whose electric potential of the reduction reaction on the goldelectrode surface was more negative than on the glassy carbon electrode, with thepossibility of forming Cu(Ⅲ) complex on its surface. The simulate chemical coatingresearch has shown that its reversible reoxidation reaction is result of the transferring oftwo single electron, and forming Cu(Ⅰ) complex. We also found out that the influenceof adding triethanolamine (TEA) in the plating solution to Cu(Ⅰ) complex was notsignificant, and it can only restore the more negative electric potential.At last, we used the atomic force microscopy techniques and electrochemicalanode dissolution method in the research of the velocity of electroless deposition, andconfirmed that the velocity of Cu-DMAB electroless deposition is0.05μm/min, and thereaction induced time is30seconds. And the researches of spontaneous decompositionof chemical copper plating pool system and controllable electroless deposition systemhave shown that the coating film from the latter has high Cu(111) content, and thechanging of reductant’s concentration has no effect on the crystal texture of the obtainedcopper. The comparison research of original battery structure has shown that theoxidation of reductant is the major limited step during the precipitation, and thecatalysis of copper to the oxidation of DMAB is better than gold; at the same time, theresearch has also shown that mixed potential theory is not applicable to the electrolesscopper system using DMAB as reductant. During precipitation, current efficiency can reach over80%in a couple of minutes at the beginning, which means that the half cellcontained copper still has side reactions, and these reactions are more obvious at thebeginning of the process. The research on triethanolamine has confirm its catalysis onthe oxidation of DMAB; and it can improve the current efficiency of electroless coppersystem.