Fabrication And Microstructure Research Of Full IMCs Micro-joint With The Aid Of Thermal Gradient

With the development of microelectronic products towards multi-functional,high-density and micro-scale,the manufacturing technology of 2-dimensional?2D?Integrated Circuit?IC?is gradually approaching the physical limitation.The packaging of 3-dimensional?3D?TSV?Through Silicon Via?becomes one promising solutionsin to break through the physical limitation and continuously extend Moore's law in microelectronic industry.In the next few years,the micro solder-joints down size will be reduced to about to 10?m in 3D TSV package,which will cause new reliability problems:The stack chip bonding heating will collapse remelting the remelting solder of the l lower level chip;As micro solder-joints down size,it will bear more thermal stress in the process of thermal service,which is coupled with the proportion of IMCs,and aggravates the early failure of the micro-joints.Intermetallic Compounds?IMCs?is frequently used as bonding materials for solder joints.They have the properties of high temperature,high hardness,high strength,and strong fatigue resistance.If all the filler metals in the solder all converted to IMCs,the problem of the micro-joints scale decreasing to less than 10?m can be solved.In typical micro-joints IMCs,Ni₃Sn₄ has the advantages of high melting temperature,stable single-phase constitution and stronger mechanical strength compared with other two IMCs?Cu₆Sn₅ and Cu₃Sn?.More importantly,Ni₃Sn₄ intermetallic is only one reaction product during liquid-solid reaction of Ni and Sn solder under 300°C,which avoids the reliability defects of the multiphase IMCs structure and phase change cracks and cavities in the reaction between Cu and Sn.Therefore,Ni₃Sn₄ should be more favorable to work as micro-joints material.However,the long bonding time to produce fully Ni₃Sn₄ composed micro-joints is still a critical issue due to low Ni dissolution rate and slow Ni₃Sn₄ growth.For this problem,this paper intends to study the rapid fabrication and microstructure research of full IMCs micro-joints with the aid of thermal gradient.The Ni/Sn?10?m?/Ni sandwich structure simulation samples were prepared by high-precision fixture.Then,full Ni₃Sn₄ micro-joints were rapidly fabricating by Temperature Gradient Transient Liquid Phase?TG-TLP?bonding.In addition,the microstructure evolution of interface Ni₃Sn₄ was observed in the fabrication process,the rapid growth of interface Ni₃Sn₄ under thermal gradient was analyzed,the mechanism of rapid formation of Ni₃Sn₄micro-joints was revealed,and the mechanical and electrical properties of Ni₃Sn₄ micro-joints were characterized.By observing the microstructure of interface Ni₃Sn₄ during the formation of the full Ni₃Sn₄ micro-joint,it can be found:In the process of TG-TLP bonding,the interface Ni₃Sn₄at the hot and cold ends showed asymmetric growth,showing the thickness of the cold end and the thickness of the hot end.The IMC morphologies represented rod-like and block-like shape at the cold end,and rod-like shape at the hot end,and with the increase of bonding time the block gradually increases and the bar decreases,this phenomenon is consistent with Ostwald maturation theory.By constructing the kinetic equation,it is concluded that the growth of cold end interface Ni₃Sn₄ in the process of TG-TLP bonding obeys the linear rule and is controlled by the reaction.The growth of hot end interface Ni₃Sn₄ is controlled by grain boundary diffusion.Under the action of temperature gradient,Ni atoms dissolved into liquid Sn at the hot end of Ni matrix continue to migrate to the cold end,providing sufficient Ni atomic flux for the rapid growth of Ni₃Sn₄ at the cold end interface.In addition,comparing with the traditional Transient Liquid Phase bonding?TLP bonding temperature maintained the same temperature as the hot end temperature of the TG-TLP bonding?,TG-TLP bonding is nearly three times faster than that under conventional TLP bonding.The tensile testing was carried out to estimate the joint mechanical property:The tensile strengths of the Ni₃Sn₄ and Sn micro-joints were measured as 180.8 MPa and 97.3 MPa,respectively.Apparently,the former possesses higher tensile strength.A resistance tester was performed to examine the electrical resistivity of the Ni₃Sn₄ micro-joints,the Ni₃Sn₄.micro-joints electrical resistivity was obtained as 5.993??·cm higher than Sn micro-joints 5.834??·cm.The results show that the Ni₃Sn₄ micro-solder joint formed by TG-TLP bonding has the characteristics of reliable single-phas,high temperature performance and rapid fabrication,can solve the reliability problem that the micro-joints scale is about to reach 10?m.Consequently,this TG-TLP process can provide a promising solution to stack 3D TSV chips.