Mechanism Of Effect Of POSS Enhanced Particles On The Morphology Of Intermetallic Compounds In Sn3.5Ag/Cu Interface

Accuracy With the development of micro-electronic packaging technology,the size of solder joints is getting smaller,increasing the volume fraction of IMCs（Intermetallic compounds）formed in the metallurgical reaction between solder and printed circuit board,and the reliability of the electronic devices would be significantly affected.Although the behavior of interfacial IMC growth has been extensively investigated,there is no definitive conclusion about the growth behavior and coarsening behavior of interfacial IMC in the metallurgical reaction or solid-phase reaction process of lead-free solder joint.Besides,as an reinforced particle,POSS can improve the performance of lead-free solders.However,there is still a lack of research on the growth behavior of POSS-reinforced interfacial IMC formed in metallurgical reaction.To make up for the deficiencies in previous researches,this research aims at the interfacial reaction between Sn-based lead-free solder and polycrystalline Cu pad.A model considering the morphology effects based on the grain boundary diffusion theory to describe the morphology evolution,growth behavior and coarsening behavior of the interface IMC is presented,and the mechanism of the influence of POSS-reinforced particles on the interfacial IMC is revealed.In this paper,the Sn3.5Ag filler was used as the research object,and the composite filler metal is prepared adding 3wt%（Polyhedraloligomeric silsesquioxane,POSS）as the reinforcing particles by mechanical mixing method.A method was designed to obtain the intermetallic compounds in the liquid phase reaction of two kinds of solders in the process of welding.By analyzing the morphology of these reactants,the growth behavior of the interface IMC formed by the tin filler and polycrystalline Cu pad was revealed in the process of liquid phase reaction.In addition,after the welding spot was cooled then solid-phase aged,the morphology evolution,growth behavior and coarsening behavior of the interface IMC between the tin filler and polycrystalline Cu solder are revealed by analyzing the interface IMC,and the effect mechanism of POSS reinforced particles on interfacial IMC in the whole interface reaction was revealed.The results show that in the interfacial reaction process,Sn3.5Ag and Sn3.5Ag+POSS solder and polycrystalline Cu form a round scallop-like Cu₆Sn₅interface in liquid-phase reaction stage,and gradually planarize in the solid phase reaction stage.In these reactions,the interface IMC morphology will be affected by temperature,reflow time,grain boundary diffusion rate and concentration gradient between the interfaces.In liquid-phase reaction stage,the interface IMC are controlled by the curing effect.In air-cooled solidification stage and solid-phase reaction stage,the interface IMC are controlled by grain boundary diffusion.In addition,the comparison data of different solders shows that during the remelting process,the interface IMC tend to grow from the grain boundaries.For the Cu concentration gradient changes slowly between the interfaces,quite a amount of IMC grown on the Sn3.5Ag bump interface,resulting in a large amount of IMC grown on the Sn3.5Ag bump interface.This mechanism makes welding temperature have little effect on the coarsening rate of IMC.However,the addition of POSS particles increases the binding energy of the Cu atoms passing through the interfacial IMC grain boundary,making it easier for interfacial Cu₆Sn₅ to grow in the grain diameter direction of the IMC.This mechanism significantly promotes the decrease of the concentration gradient between the interfaces,thus reducing the period between remelting and solid phase.This mechanism also makes welding temperature have more effect on the coarsening rate of IMC.Under the influence of those effects,the increase of remelting temperature and the increase of remelting time will make the coarsening growth of IMC in the interface of Sn3.5Ag+POSS solder joints much more slower than the Sn3.5Ag solder joint interface IMC during the aging process.