Technical Investigation For Electroless Copper Plating Using Glyoxylic Acid As Reducing Agent

As a kind of surface treatment technology, electroless copper plating is widely used in field of electronics, mechanical, aerospace and other industries, because its plating has many advantages like good scattered ability, unconspicuous edge effect, high conductivity, etc. With the continuous development of the electronics industry, especially the micro-electronic technique, more stringent requirements are put forward to electroless copper plating applied in this field. Currently, formaldehyde and sodium hypophosphite are widely used as reducing agent of electroless copper plating, and have high technical maturity. However, considering the problem of environmental factors and plating quality, a more excellent reducing agent is needed urgently. Compared with other reducing agents, the application prospect of glyoxylic acid is very wide, and it is more likely to replace formaldehyde and sodium hypophosphite. But, its process needs further study.Specific to the electroless copper plating applied in electronics industry, the conductive treatment of plastic material was mainly researched. The parameters of pretreatment for insulating material was optimized as same as the electroless copper plating using glyoxylic acid as reducing agent.Firstly, polysulfone was selected by comparing the performance parameters, which had excellent mechanical and electrical properties. In the process of pretreatment for polysulfone substrate, the coarsening method was optimized. When the substrate was processed by organic solvent swelling (dichloroethane40%and absolute ethyl alcohol60%by volume) for1.5minutes, then chemistry coarsening (CrO3400g/L,98%H2SO4250mL/L) for5minutes under60℃, the coarsened surface had better uniformity and hydrophily. By comparing the effect of washing temperature after sensitization process on plating integrality, washing temperature was determined as40℃Secondly, the component of plating bath was determined by experiment, which was Cu(NO3)2·3H2O20g/L, CHOCOOH·H2O15g/L, Na2EDTA45g/L, K4Fe(CN)6·3H2O10mg/L, bpy10mg/L, pH13, and processing temperature was55℃. Through single factor experiment, the effect of process parameters on deposition rate, stability of bath and resistivity of copper film was investigated. In the research of relationship between deposition rate and resistivity, it was found that the resistivity decreased with the increasing deposition rate. The resistivity minimum of copper film was2.38μΩ·cm. In addition, a component analysis of copper film plated under optimized process parameters was made, which showed the component of the plating was copper element only. If pH value was12or less, the oxygen element content of plating would increase. This showed the reduction ability of glyoxylic acid was so weak that made the side effects more likely to occur. As a result, CU2O impurities generated by side effects made the plating black and dark. When the pH value was about12.5～13, the uniformity and compactness of deposited copper film was better.