Researchonthe Process Of Acidic Cyanide-freebright Silver Electroplating

Silver has been widely employed in the fields of electronic packaging and medical equipment due to its excellent solderability,electrical and thermal conductivity,waveguide receiving and antibacterial properties.In this thesis,a strong acidic cyanide-free silver electroplating bathwas developed in order to reduce the environment pollution causedbycyanide silver plating process.By using the modern analytical instruments,the commercial cyanide-freebright silver plating bath was assumed to be composed of silver mesylate,methanesulfonic acid,disodium phosphate dodecahydrate,isopropanol,2,4-dihydroxybenzoic acid,etc.Then,the content of each component was quantitatively analyzed.And the veracity of the above results were validated by electrochemical measurements and X-ray diffraction tests.Most importantly,a set of analytical procedures for general baths was obtained.However,the mirror bright silver coating can not be observed asthe brightenerwas mising in the analysis result.According to the analysis results,three kinds of adsorbing scale inhibitor,including phytic acid,HEDP and sodium tripolyphosphate,were selected as the brighteners on the Hull cell test.The influence of these three additives on the performance of the coating and plating bath was characterized,and the results revealed that the surface adsorption of these additives on the cathode had a great impact on the crystalline orientation of the coating.To a certain extent,the three additives also increased the overpotential and led to the grain refining as well as hardness,interal stress,and brightness.Inorder to broaden the brightening range and find the best additive combination,the effect of pairwise combination among phytic acid,HEDP and sodium tripolyphosphate was measured by the Hull cell test at at pH=1.0,45℃,200 rpm,2.0 A/dm~2.It was found that the brightening range became the broadest and the coating surface was fine and smooth through the addition of 300 mg/L of HEDP and 0.75 ml/L of 50%phytic acid.The optimized bath composition is composed of 80.00 g/L of silver mesylat,61.00 g/L of methanesulfonic acid,13.50 g/L of disodium phosphate dodecahydrate,50.00 ml/L of isopropanol,3.00 g/L of2,4-dihydroxybenzoic acid,200 mg/L of MPEG-600,20 mg/L of APEG-20000,0.75 ml/L of50%phytic acid and 300 mg/L of HEDP.The coating quality and electrolyte performance were tested,and the results show that the performance of the self-developed plating solution is close to the commercial one.The plating solution is stable and volatile,and can be stored for a long time.Coating adhesion and internal stress are met and the hardness of the coating is about 140 HV.When the current density is 2.0 A/dm~2,the plating speed is about 1.835μm/min,the current efficiency of anode and cathode is more than 90%.The self-developed plating solution can satisfy some specified application requirements.