Electromagnetic Induction Heating Co/Sn Interface Reaction And Its Application To Micro-joint

The TSV 3D IC packaging technology,with high integration and low power consumption,has become an advanced packaging technology.The packaging technology usually employs thermal compression bonding,but the problem of high stress and strain caused by global heating exists.Electromagnetic induction heating bonding has the advantage of selective heating and has become a potential solution to this problem.Metal Cohas good conductivity and anti-electromigration ability,and is considered a potential solder pad material in the next few years.This study investigated the solid-liquid interface reaction of Co/Sn under electromagnetic induction heating and analyzed the evolution and growth behavior of interface IMC（Intermetallic Compounds）morphology during the solid-liquid reaction,as well as the effect of electromagnetic induction heating on IMC growth.Co/Sn was applied to IMC micro-joint by induction heating bonding,and the interface reaction during the formation of the micro-joint and its mechanical properties were characterized.The research results are as follows:（1）Compared with the commonly used Cu/Sn and Ni/Sn solid-liquid reactions,Sn has good wetting on Cointerface,and the growth rate of interface CoSn₃reaches 2.38μm/min,which is more than 2.5 times faster than the growth rate of Cu/Sn and Ni/Sn interface IMC.This is related to the morphology,scale,and growth mode of CoSn₃grains.Compared with direct heating and induction heating Co/Sn solid-liquid reaction,induction heating promotes faster growth of Co/Sn interface CoSn₃,and there are more large-scale CoSn₃grains.The main reason is that electromagnetic stirring accelerates the flow of reactive atoms in liquid Sn.Mechanical tests show that the elastic modulus and hardness of CoSn₃are slightly lower than those of Cu₆Sn₅and Ni₃Sn₄,showing good toughness.（2）In the electromagnetic induction heating Co/Sn solid-liquid interface reaction,the growth of interface CoSn₃shows a trend of rapid growth followed by a slowdown.The morphology of CoSn₃grains changes from initial upright thin-sheet shape to rapidly coarsened sheet shape,and the morphology change slows down after 4 minutes.The growth mode of the interface CoSn₃is that the square-shaped CoSn₃grains grow in a vertical stack,and the CoSn₃grains are filled with filler material.This growth mode allows the interface Coatoms to quickly enter the filler material and participate in the interface reaction to promote the growth of CoSn₃.The coarsening of CoSn₃grain shape exists in both the self-growth and the merging growth of grains.The CoSn₃layer at the interface of 260℃and 280℃is controlled by volume diffusion and reaction,respectively.（3）Using the electromagnetic induction bonding method based on the Co/（10μm）Sn/Costructure,CoSn₃micro-joint were prepared at 260℃and 280℃in 90s and 70s,respectively.This is nearly 20 times faster than the traditional Cu/Sn system and Ni/Sn system CoSn₃micro-joint,mainly due to the stack growth mode of square-shaped IMC grains and the growth by quick merging of grains.The shear strength of CoSn₃micro-joint is 32Mpa,showing good mechanical properties required for CoSn₃micro-joint.