Preparation Of Multilayered Sn/Ag Film By Electrodeposition And Its Interface Evolution

As a new type of solid-state semiconductor illumination source,Light Emitting Diode（LED）is widely used in indoor lighting,backlight and color screen.However,the problem of low light output rate seriously affects the reliability of LEDs and limits the development of LEDs.At present,effective ways to improve LED light extraction rate mainly include metal film reflection technology,transparent substrate technology and surface microstructure technology.Among them,the metal film reflection technology represented by Ag and its alloys has been widely concerned by researchers in this field because of its convenience in mass production,and has obtained a lot of research and development.However,this technology has strict requirements on the quality of the metal reflective layer,and vacuum sputtering（deposition）equipment is usually used to prepare a satisfactory film layer.However,this process is complicated and costly,limiting the application of such a reflective layer.Therefore,the study of metal reflective layers with simple structure and low cost and high reliability is the key to expanding the application of this system in the field of LED metal reflective layers.Since Ag is easily oxidized and vulcanized in a high-temperature,sulfur-containing environment,and the reflectance is severely lowered,improving the reliability of the Ag-based reflective film material is the key to preparing a metal reflective layer.In this paper,a certain thickness of Sn and Ag coatings are deposited on the substrate by step plating,and the composite coating is annealed to obtain the intermetallic compound Ag3Sn.On the basis of ensuring the high reflectivity of the metal reflective layer,the anti-vulcanization performance is improved.On this basis,this paper deeply studies the effects of annealing temperature,annealing time and coating sequence on the microstructure and properties of the coating,and studies the growth kinetics of Ag3Sn in the solid phase reaction zone of Sn/Ag interface to control the coating structure and performance.The main findings of the paper are as follows:（1）The study obtained a bright tin plating solution with stannous sulfate as the main salt and a high stability silver plating solution with nicotinic acid as the complexing agent,silver nitrate as the main salt and 2,2 bipyridyl as the additive were obtained.And optimize the optimal bath composition and plating process parameters for both.Among them,the tin plating solution has high dispersibility,and can prepare a bright and dense tin plating layer;the silver plating liquid is non-toxic and environmentally friendly,and the obtained silver plating layer is close to silver cyanide plating.（2）Based on the experimentally obtained tin plating solution and silver plating liquid,a highly reflective and sulfur-resistant Sn/Ag metal reflective layer was successfully prepared by a heat treatment process.In order to better control the coating to predetermine the film structure,the effects of annealing temperature,annealing time and coating sequence on the microstructure and properties of the coating were investigated.The experimental results show that increasing the annealing temperature can effectively promote the formation of Ag₃Sn,and the effect of prolonging the annealing time on the growth of Ag3Sn is not significant.The formation of Ag₃Sn will reduce the reflectivity of the coating to a certain extent,but greatly improve the corrosion resistance of the coating.In addition,changing the plating sequence will result in different coating structures under the same annealing process.This may be caused by the formation of tin oxide on the surface of the plating during the electroplating of tin,which hinders the migration of Sn-Ag interface atoms during annealing.（3）Based on the influence of annealing temperature and annealing time on the coating,the kinetics of Sn/Ag interface solid phase reaction annealing at 120°C²00°C was studied.The experimental results show that the process follows the parabolic reaction kinetics,and the reaction equation is calculated as k=5×10^-8exp[-15.2/（RT）].