Wetting Behavior And Interfacial Structures Of SnAgCu-xTi On Silica Glass And Si Surface

Monocrystalline Si,as one of common semiconductor materials,which is widely used in electronic devices,solar cells,microfluidic devices.In these applications,silicon and silicon-based materials often involve the wettability issue of the solder and the base materials during the joining process,while the wettability of silicon by the tin-based solder is affected by many factors（such as temperature,atmosphere,surface state,etc.）,so that,how to improve the wettability of silicon by tin-based solder,and further understanding of its interfacial microstructure and wetting mechanism,which is crucial for the silicon and silicon-based materials to obtain excellent brazed joints.In addition,it is worth noting that silicon is very sensitive to oxygen,the surface of Si and some Si-contained material are easily oxidized to form a SiO₂ oxide film.Therefore,the study of the wettability of SiO₂ by the Sn-based solder is very essential.It can not only show the practical electronic packaging environment of the Si substrate,but also can realize the regulation and optimization of the interfacial structures of Si and Si-based materials.In this thesis,by adding the active composition Ti into SnAgCu,the modified sessile drop method was used for studying the wettability of SnAgCu-x Ti（x=1,3 wt.%）on amorphous silica and monocrystalline silicon（100）surfaces under high vacuum conditions at 800-900℃.The previous research results show that the wettability improvement of SnAgCu-x Ti/Si system is not significant,further two schemes are proposed:（1）the surface of monocrystalline silicon was coated with Ag or Cu by ion sputtering method,and the wettability of SnAgCu on the coated surface at 800℃ was studied;（2）Wettability of the monocrystalline silicon（100）by Sn-x Al（x=2.4,50 at.%）and Al at 900℃ was studied.Using SEM,EDS,XRD,XPS,optical microscopy and the other analytical methods,meanwhile,in combination with the theories analysis of interface thermodynamics and spreading model,the wetting behavior,the interfacial structure,the spreading mechanism and spreading dynamics of the system were revealed.The main results of this thesis are as follows:（1）In the SnAgCu-x Ti（x=1,3 wt.%）/SiO₂ system at 800-900℃,by additions 1 wt.%and 3 wt.%Ti into SnAgCu,the wettability was improved significantly.SnAgCu-x Ti/SiO₂ system has two spreading stages:rapid spreading stage and linear spreading stage,Ti₅Si₃ and TiO are firstly precipitated in the rapid spreading stage,while only TiO is precipitated in the linear spreading stage.The system is a typical reactive wetting system,and the spreading kinetics can be described using the reaction product control（RPC）model.However,the final wettability was determined both by the wetting character of reaction products and the Ti-O adsorption at interface.（2）At 800-900℃,SnAgCu-x Ti（x=1,3 wt.%）/Si system is an inert wetting system with certain dissolution,although the active component Ti by introducing into SnAgCu,to some extent,the wettability of the system can be improved,but the improvement effect is not obvious;the role of Ti in the SnAgCu-x Ti alloy is not at the interfacial chemical reaction or chemisorption,but is the enhanced dissolution of the Si substrate.the dissolved Si forms a pyramidal structure at the interface through the dissolution precipitation mechanism and the micro-mask mechanism;the appearance of the"pyramid"structure does not improve the wettability,but instead pinning of the triple line.The pinning action by the pyramidal structure caused discontinuous,stepwise variations in the wetting curve.With the Ti concentration or the experimental temperature increasing,the solubility of Si in the solder was increased,which limits the formation of the interfacial"pyramid"structure.（3）After Si surface was metallized,the system is a inert wetting system.The improvement of the wettability of the system after surface metallization is mainly due to the increase of solid surface energy;At 1100℃,the coating metal dissolves and diffuses into the surface of the substrates,the oxide film on the surface of the substrate was removed,therefore the wettability of the system is improved.（4）At 900℃,the role of Al in Sn-x Al（x=2.4,50 at.%）/Si system is to increase the dissolution of Si by segregation at the liquid/solid interface.The effect of dissolution on the wettability of the system is related to the amount of dissolution.Only within a specific range of dissolution,dissolution can act as a spreading driving force to improve the wettability of the system;In addition,the evolution of interface geometry due to dissolution should also be considered for the effect of dissolution on wettability of the system.As in the Al/Si system,the formation of crater is harmful to the wetting process,and which is related to the Marangoni effect induced by solute concentration gradient in the inner of drop.Generally,the scale law indicates that the spreading in this study satisfies the description of the hydrodynamic dynamic model,the spreading in this study was limited by the viscous dissipation.In Sn-x Al/Si system,the initial deviation of scale law is due to the transport of Al from inner drop to the triple line.In Al/Si system,the latter stage of spreading is affect by the convection in the inner of drop.In summary,the research results has certain theoretical guiding significance for the electronic packaging and preparation of metal matrix composites.