Study On Synthesis Of Environmental Friendly Gold Complex And Its Electroless Gold Plating Process

In recent years,the rapid development of electronic information industry has generated a huge demand for printed circuit board(PCB).Chemical gilding process is an important surface treatment technology in PCB manufacturing process,which provides a protective layer with excellent electrical conductivity and corrosion resistance for circuit board.The traditional chemical gold plating system is cyanide gold plating system,which has the advantages of high stability of plating solution,bright appearance of gold plating products and good uniformity of plating layer.However,CN-in its plating solution will cause great harm to human body and environment,so a new non-cyanide gold plating system is needed for PCB production.In order to solve the problem of environmental hazards of non-cyanide gold plating system,a new type of non-cyanide gold complex was synthesized by selective reduction method and coordination exchange method using HAuCl4 as the parent material and iodine and thiourea(hereinafter referred to as Tu)as non-cyanide ligands.Then the molecular formula of the sub-gold complex was determined by infrared spectroscopy,ultraviolet spectroscopy,thermogravimetric analysis,conductivity measurement and elemental analysis.In the next step,the best process conditions for preparing intermediate compound AuI and target product are obtained through experiments.Finally,the orthogonal experiment was designed to select the best technological conditions for the new type of gold-plating system of sub-gold complexes and analyze the gold-plating quality of the gold-plating process in the experiment.The specific research results are as follows:(1)A new type of sub-gold complex was synthesized,analyzed and characterized.According to its infrared spectrum analysis,ultraviolet spectrum analysis,elemental analysis,thermogravimetric analysis and conductivity measurement results,the chemical formula of the complex is determined to be[Au(Tu)2]I,and the molar conductivity is 9.6 X 10-4 S·m2·mol-1.The relation of process parameters that affect the synthesis test results of the target product[Au(Tu)2]I is that the concentration ratio is greater than the concentration temperature,the molar ratio of thiourea to gold is greater than the concentration of thiourea.The concentration of thiourea is 50 mg/mL,the molar ratio of thiourea to gold is 5:1,the concentration temperature is 45?,and the concentration ratio is 4.5,which is the best synthesis condition in the experiment.(2)The experimental results of synthesis of intermediate Aul show that the relationship of process parameters affecting the synthesis of AuI is that the operating temperature is higher than the concentration of chloroauric acid solution and higher than the concentration of potassium iodide solution.The experimental operating temperature is 5?,the concentration of chloroauric acid solution is 30 mg/mL,and the concentration of potassium iodide solution is 25 mg/mL,which is the best synthesis condition in the experiment.(3)The experimental results of chemical gold plating using complex[Au(Tu)2]I as gold source show that the relationship of influencing factors of gold plating performance under this gold plating system is that the concentration of gold salt is greater than the temperature of gold plating solution,the plating time is greater than the concentration of complexing agent thiourea,and the pH value of plating solution.The best experimental process parameters are gold salt concentration of 3 g/L,gold plating solution temperature of 55?,pH value of 3.5,complexing agent thiourea concentration of 12.5 g/L,and plating time of 20 min.Under the experimental conditions,the gold-plated layer of the plated plate has good color and bonding strength.The plating thickness of the plating plate is stable at 0.11 microns.Scanning electron microscope was used to observe the coating,which was compact.The corrosion resistance test and weldability test of the coating are qualified.In this study,the non-cyanide gold complex synthesized under the optimal conditions was used to study the electroless gold plating process.Under the experimental conditions,the electroless gold plating process can basically reach the level of mature process.Compared with the existing process parameters,the non-cyanide chemical gold plating process in this study has the advantages of easy control of the thickness and quality of the gold plating layer and low production energy consumption.At the same time,in the production process,compared with the traditional gold plating process,the non-cyanide gold plating process in this study uses chemicals that have less impact on the environment,and the reaction waste is easier to be treated to meet the emission standards,thus having good industrial application value and prospect.