| Since silver has the advantages of higher conductivity,lower young’s modulus,higher potential stability and higher reflectivity,it is widely used to fabricate electrode,high-Q capacitors and inductors,reflective film,low-delay connection material in MEMS devices,which need micro-processing technology to achieve the patterned Ag film.The patterned Ag film is generally achieved by the dry process or electroplating using SU-8 negative photoresist as a mask material.The dry process has the disadvantages of low material utilization efficiency,slow deposition and etching speed,which limits its application in the thick silver film.UV solidified SU-8 is generally acknowledged to be difficult to strip.The paper tries to fabricate the patterned silver film by electroplating using the positive photoresist as the electroplating mold material.The effect of the bath component on the stability of the thiosulfate bath is investigated.The optimal composition for the stable thiosulfate bath from orthogonal experiment is 3042.5 g/L AgNO3,200250 g/L Na2S2O3,and 4045 g/L K2S2O5,and the pH value is 56.Then,different addictives are tried to improve the glossiness of the coating.The effects of pulse plating and current density on the glossiness and surface morphology of the Ag film are studied.The optimal electroplating processs for the sodium thiosulfate bath has the current density of 13 mA/cm2 and pH of56.The effects of pH value,current density and temperature on the coating glossiness,surface roughness,and surface morphology are studied for low cyanide bath.When the pH value is reduced from 8.6 to 7.6,the coating performance is almost unchanged.However,when the pH value decreases from 7.6 to 6.8,the coating performance decreases remarkably.The optimum plating conditions for the cyanide bath are as follows:the pH value is 7.6,the temperature is 25℃,and the current density is 2 mA/cm2.The effects of current density and pulse plating on the properties of the coating for potassium thiocyanate bath are studied.The roughness of coating decreases with the increasing current density,and the optimum current density is 68mA/cm2.Compared with direct current electroplating,the grain size of the coatings obtained by pulse plating is smaller and the grains are denser.The optimized parameters for pulse plating are as follows:the average current density is 68mA/cm2,the duty ratio is 1/16,and the pulse period is 20ms.The stability of the above three electroplating baths and their compatibility with the micro-processing process are compared summarily.It is found that low-cyanide bath and potassium thiocyanate bath are more stable than sodium thiosulfate bath.The acid potassium thiocyanate bath and sodium thiosulfate bath are more compatible with the micromachining process than low-cyanide bath.Weakly alkaline low-cyanide plating bath can also be used to achieve the patterned Ag film,but not thick patterned Ag film.Both sodium thiosulfate bath and low-cyanide bath can be used for the patterning thin Ag film with high glossiness and low roughness,while potassium thiocyanate bath can be used to produce thick Ag film. |
