Research On Interface Behavior Of Sn/Ni System With Micro-Interconnect Structure

With the continuous shrinking of electronic chips and the gradual diversification of functions,the performance requirements for micro-interconnect solder joints of the chips are getting higher and higher.In electronic packaging,micro-interconnect solder joints are usually composed of Sn solder and Cu substrate.During the service process of Sn/Cu joints,thicker Cu₆Sn₅and Cu₃Sn layers will be formed at the interface.The excessively thick intermetallic compound(IMC)layer at the solder joint interface is brittle and hard,which will cause cracking failure of the interconnect solder joint.Therefore,a thin Ni sheet is generally used as a diffusion barrier for the Sn/Cu joint,which slows down the growth of the IMC layer of the Sn/Cu joint.In the selection of Ni substrate,there are many grain boundaries of polycrystal Ni,while single-crystal Ni has almost no grain boundaries.The microstructures of single-crystal Ni and polycrystal Ni are different,and its influence on the interface behavior of Sn/Ni joints is not yet known.Therefore,this subject uses reflow soldering to form Sn-x Ni/PC Ni and Sn-x Ni/SC Ni joints with polycrystal Ni(PC Ni)and single-crystal Ni(SC Ni)substrates and Sn-x Ni solder(x=0,0.05,0.1).The growth behavior of liquid IMCs grains and the microstructure evolution of the solid-phase interface IMCs layer in the Sn/PC Ni and Sn/SC Ni joints under different as-reflowed time and thermal aging times were studied,and the Sn-x Ni/PC Ni,Sn-x Ni/SC Ni interface growth behavior.It provides theoretical guidance for the selection of Ni diffusion barrier layer and its interface growth behavior in electronic packaging.The research results are as follows:(1)The interface phase of Sn-x Ni/PC Ni joints(x=0,0.05,0.1)were rod-shaped Ni₃Sn₄phase at different time of as-reflowed at 260°C and thermal aging at 180°C,while the interface phases of Sn-x Ni/SC Ni joints(x=0,0.05,0.1)were layered Ni Sn₄phases.The Ni Sn₄phase was a metastable phase in previous studies,but when a SC Ni substrate was used in this experiment,the interface phase was stable as the Ni Sn₄phase.In the initial stage of the liquid phase reaction,the growth behavior of the IMCs of Sn/PC Ni and Sn/SCNi joints were the behavior of grain maturation.With the extension of the as-reflowed time,the growth behavior of IMCs changes to the grain merging behavior.(2)The interface layer of Sn/PC Ni and Sn/SC Ni joints became thicker with the extension of thermal aging time,and the thickness of the Ni₃Sn₄layer was significantly thicker than that of the Ni Sn₄layer.With the extension of the thermal aging time,the Ni₃Sn₄layer at the interface of the Sn/PC Ni joint gradually becomes dense and flat.With the extension of the thermal aging time of the Sn/SC Ni joint,the interface Ni Sn₄layer gradually becomes thicker,and at the same time,the Sn atoms will form the Ni Sn₄phase with the?phase on the top of the SC Ni substrate,forming a thinner diffusion layer.The PC Ni substrate mainly provides Ni atoms to the interface through grain boundary diffusion,while the SC Ni substrate mainly provides Ni atoms to the interface through lattice diffusion.Combined with the interface growth kinetics,analysis found that the growth of the Ni₃Sn₄layer was mainly controlled by diffusion elements,while the growth of the Ni Sn₄layer was mainly controlled by the reaction rate.(3)When the Sn-x Ni/PC Ni joints were as-reflowed for 5 min,the Ni₃Sn₄grain size of the Sn0.05Ni/PC Ni joint was the smallest.When the thermal aging time was the same,the thickness of the Ni₃Sn₄layer of the Sn0.05Ni/PC Ni joint was the thickest,and the thickness of the Ni₃Sn₄layer of the Sn/PC Ni joint was the thinnest.When the Sn-x Ni/SC Ni joints were as-reflowed for 5 min,the thickness of the Ni Sn₄grain of the Sn/SC Ni joint was the thinnest.When the thermal aging time was the same,the thickness of the Ni Sn₄layer of the Sn0.1Ni/SC Ni joint was the thickest,and the thickness of the Ni Sn₄layer of the Sn/SC Ni joint was the thinnest.The thickness of the Ni Sn₄layer of the Sn-x Ni/SC Ni joints were less than the thickness of the Ni₃Sn₄layer of the Sn-x Ni/PC Ni joints,and the thickness of the Ni Sn₄layer of the Sn-x Ni/SC Ni joints were relatively thin and uneven.