Investigation On The Reliability Of ZrC Reinforced Sn-9Zn Composite Solder Joints During Thermal Field

As lead-free solder become an inevitable trend in the electronics industry,the research of lead-free solder has become a hot topic in the field of electronic packaging.Among them,the melting point of Sn-Zn eutectic alloy is 198.5°C,which is the closest to Sn-Pb solder(183°C).The use of Sn-Zn alloy as a substitute eliminates the need to develop high-temperature brazing equipment,printed circuit boards,and soldered electronic components,which can significantly reduce the cost of the lead-free solder conversion process.In addition,Zn is cheap,non-toxic,and has a relatively abundant storage.The addition of other elements in the Sn-Zn binary alloy can further improve the properties of the solder and is also widely used in the electronics industry.In this paper,the composite solder is prepared by adding different ZrC nanopariticles(0.03 wt.%,0.06 wt.%,0.09 wt.%,0.12 wt.%).The effect of trace ZrC on the wettability,microstructure and mechanical properties of Sn-9Zn composite solder alloy joints was investigated.The results indicated that the wettability of the Sn-9Zn based composite solder alloy was improved and the microstructure was refined by adding appropriate amount nanoparticle ZrC.The microstructure of Sn-9Zn based composite solder alloys consists of primary Sn and Sn-Zn eutectic,and the excellent wettability and refined microstructure can be obtained by adding about 0.06 wt.%ZrC.The interfacial intermetallic compounds(IMC)layer in the Sn-9Zn based composite solder alloy joints consists of Cu5Zn8 and Cu6Sn5.IMC layer thickness of Sn-9Zn based composited solder alloys joints is increased with increasing ZrC content.The tensile strength and the shear strength of Sn-9Zn based composite solder alloys joints relate to the ZrC content,and the maximum mechanical properties of solder joints are obtained by adding about 0.06 wt.%ZrC,and the fracture mechanism of the Cu/Sn-9Zn-(0-0.09)ZrC/Cu solder joints is ductile fracture.The influence of aging temperature on the microstructure and mechanical properties of Sn-9Zn and Sn-9Zn-0.06ZrC solder joints was investigated.The microstructures of Sn-9Zn and Sn-9Zn-0.06ZrC solder joints are coarser with the increase of aging temperature and the microstructure of Sn-9Zn-0.06ZrC solder alloy is finer compared with Cu/Sn-9Zn/Cu solder alloy.The IMC layer thickness of the Sn-9Zn and Sn-9Zn-0.06ZrC solder joints showed an increasing trend during the aging process.The IMC interface of Sn-9Zn solder joint gradually transforms from a flat shape to a zigzag shape and grows toward the solder and the Cu substrate,respectively.While the IMC interface of Sn-9Zn-0.06ZrC solder joint gradually tends to be thicker and flat.,The β-Sn phase in the Sn-9Zn solder recrystallizes and burns at the aging temperature 175 °C,indicating that the aging temperature of the solder joint does not exceed 175 °C.The tensile strength of Cu/Sn-9Zn/Cu and Cu/Sn-9Zn-0.06ZrC/Cu solder joints decreased,and the dimples of tensile fractures increased in size and decreased in number with increasing aging temperature.The tensile strength of Cu/Sn-9Zn-0.06ZrC/Cu solder joints is higher under the same ageing conditions when compared with Cu/Sn-9Zn/Cu solder joints.The stable ZrC does not participate in the reaction during the aging process,and it can pin the phase boundary and hinder the diffusion of elements to improve the mechanical properties.The effect of thermal cycle on the microstructure and mechanical properties of Sn-9Zn and Sn-9Zn-0.06ZrC solder joints was investigated.The microstructure of plain solder and ZrC reinforced composite solder is coarsed with increase the number of thermal cycles,and the thickness of interface IMC layer gradually increased.The microstructure of Cu/Sn-9Zn-0.06ZrC/Cu solder alloys is finer and smaller compared with Sn-9Zn solder alloys,indicating that the ZrC nanoparticles refine the microstructure.The tensile strength of Cu/Sn-9Zn/Cu and Cu/Sn-9Zn-0.06ZrC/Cu solder joints showed a decreasing trend with increasing thermal cycles.The Sn-9Zn-0.06ZrC solder joints have higher tensile strength than Sn-9Zn because ZrC refines Cu/Sn-9Zn/Cu solder joint microstructure under the same thermal cycling conditions.The ZrC particles distributed at the grain boundary increases the grain boundary strength,and ZrC in the grain hinders the dislocation movement during the plastic deformation to make the stress distribution more uniform,thereby improving the mechanical properties of the solder joint.Finite element simulation solder joint stress concentration point at the edge of the Cu plate and solder joint.The cycle time of solder joints predicted by C-M equation was between 1500-1600,and the prediction results were in good agreement with the experimental data.The creep resistance of Cu/Sn-9Zn-xZrC/Cu solder joints under temperature and stress coupling conditions was studied.The creep rupture life of plain solder and composite solder joint is reduced gradually and the steady state creep rate is gradually increased with increasing temperature and stress.The creep rupture life of Sn-9Zn-0.06ZrC solder joints is higher than that of Sn-9Zn solder joint.The fracture patterns of plain solder and composite solder joints are changed from ductile fracture to transcrystalline fracture.Adding ZrC particles can increase solder joint creep life.The tensile creep constitutive equations of plain solder and the composite solder joints are writeen as (?),respectively.The tensile creep mechanism of Sn-9Zn and Sn-9Zn-0.06ZrC solder joints is the effects of lattice diffusion determined by dislocation climbing.