Study On The Preparation And Anti-sulfidizing Property Of Highly Reflective Conductive Sn/Ag Film

Compared with these traditional lighting sources,light emitting diodes（LEDs）which has been widely used in various lighting occasions own many advantages,such as the small volume,high reliability in bad environment and low energy loss.However,these disadvantages of LED,such as the low light output and the easily heat generation,seriously restricts its further development and applications.Because the direction of the photon emission excited by LED is omnidirectional,the reflective films can be added on the non outgoing side of LED,and the photon can be reflected to the output side to improve the light output rate and meanwhile it can also reduce the corresponding heat generation.However,during the service process of LED,the reflective film is easily poisoned by S element carried by LED devices,leading to the reflectivity decrease of Sn/Ag films.Sn/Ag reflective film has good reflectivity and meanwhile the as-formd intermetallic compounds resulting from the interfacial reaction between Sn and Ag can substantially improve its anti-sulfidizing properties.However,different arrangement of Sn atoms on different crystal plane will affect its performance of Ag film electroplated on Sn substrate.In addition,in order to promote the interfacial reaction between Sn and Ag,the external energy is needed to overcome the barrier of Sn and Ag reaction.In this paper,different methods were employed to prepare Sn substrates,and then the influence of Sn bottom layer and different heat treatment temperature on the optical and vulcanization resistance of Sn/Ag films were systematically investigated.The main contents of this paper are as follows:（1）The effects of Sn bottom layer obtained by different methods（including calendering Sn plate,bright untreated method,bright air cooling method and non bright water cooling method）on the preferred orientation,phase,morphology,reflectivity and dynamic potential polarization curve of Sn/Ag films were studied.The obtained results show that the preferential orientation,morphology,reflectivity and sulfidizing resistance of as-prepared Sn/Ag films are obviously different.Among these as-prepared Sn/Ag films,the Sn/Ag films on Sn bottom layer prepared by the bright untreated method have the highest reflectivity,and excellent sulfidizing resistance,which own the best comprehensive properties.（2）Based on the method for preparing the light electroplated Sn layer without any further treatment,the effect of Sn current density on the reflection of Sn/Ag thin films was systematically investigated.The results show that the reflectivity of Sn/Ag films is the highest when the current density of Sn plating is 2 A/dm².（3）Based on the preparation method of Sn coating and the influence of current density for electroplating Sn layer,the effects of temperature（room temperature,60℃,90℃,120℃and 150℃）on the phase,morphology,reflectivity and dynamic potential polarization curve of as-prepared Sn/Ag films were studied,respectively.The experimental results show that when the heat treatment temperature is 120℃,the intermetallic compounds（IMC）phase of Ag₃Sn and Ag₄Sn are formed in Sn/Ag film.The anti-sulfidizing property of Sn/Ag film is obviously improved at the expense of a small amount of reflectivity,and thus the Sn/Ag film with the best comprehensive properties is obtained.（4）During 150℃heat treatment,the Gibbs free energy changes of Sn-Ag system for the formation and growth of IMCs are discussed from the material thermodynamics when the nuclei of IMC is at different position in Sn/Ag films.When the nucleation position of IMC is at Sn/Ag interface,Gibbs free energy changes of Ag₃Sn and Ag₄Sn are-89.3 k J/mol and-113.3 k J/mol,respectively,which indicates that both Ag₃Sn and Ag₄Sn can be formed in the Sn/Ag layer.When the nucleation position is inside the Ag layer,the Gibbs energy changes of Ag₃Sn and Ag₄Sn are 41.79 k J/mol and-69.8 k J/mol,respectively,which indicates that the formation of Ag₄Sn are preferred.When the nucleation position is inside the Ag layer,the Gibbs energy of Ag₃Sn and Ag₄Sn at Sn layer is-29.8 k J/mol and-25.1 k J/mol,respectively,indicating that both Ag₃Sn and Ag₄Sn can be formed in the Sn/Ag layer.