Effect Of MXene Reinforcement On The Performance Of SnAgCu Lead-free Solder

SnAgCu（SAC）is one of the most widely used Pb-free solders because of its outstanding properties.However,SAC is hard to meet the requirements of industry with the development directions into miniaturization and lightweight of electronics.Incorporation of secondary phases into SAC is one of the practical measures to improve its properties.MXenes,a new group of two-dimensional layered materials,are an ideal reinforcement to SAC solder with the advantages of large specific surface area and good electrical conductivity.We have successfully fabricated a series of MXene-SnAgCu（MXene-SAC）solders containing 0.1 wt%,0.2 wt%,0.5wt%and 1 wt%MXene,respectively,via powder metallurgy route.Scanning electron microscopy（SEM）,X-ray diffraction（XRD）,etc.,were used to analyze the phase constituents,the crystal structure and the morphology of the composite solder.The Vickers hardness of composites was measured by Vickers microhardness tester.The resistivity was measured by using four-terminal method.The density was measured by using Archimedes method.The thermal diffusion coefficient was tested by laser thermal conductivity.The coefficient of thermal expansion（CTE）of composites was studied by using thermal mechanical analyzer.Likewise,we measured the melting point and wettability to represent the weldability of the composites.We also observed the IMC in the interface of solder/Cu substrate to analyze the stability of composites solder.The result showed that,the addition of MXene can refine the microstructrue of SAC composites and the grain refinement results in an increase of 11%in hardness and a decrease of 2°C in melting point.With the addition of MXene,the thermal diffusivity of the MXene-SAC increases by 70%,because MXene tends to form a thermal conductive network in solders.However,as the addition of MXene is higher than 0.5 wt%,MXene tends to be agglomerated,which decreases the thermal diffusivity.The CTE of MXene-SAC composites decreases from2.1×10^-5/K to 1.47×10^-5/K with the addition of MXene.MXene can effectively improve the wettability between SAC and Cu.The contact angle of MXene-SAC decreases from 45.1°to24.9°.The relative density and resistivity of MXene-SAC composites are about 95%,1.03Ω·mm²/m,respectively and change slightly with MXene addition.The liquid MXene-SAC solder reacts with Cu substrate to form scalloped intermetallic compound（IMC）layer during the beginning of the welding,including a Cu₃Sn layer close to Cu side and a Cu₆Sn₅ layer near solder.With the increasing time of brazing and aging,the thickness of Cu₆Sn₅ layer increases gradully and its morphology changes from scalloped to prismatic.The growth rate of IMC thickness decreases with MXene addition.Inceasing temperature leads to an increase in the diffusion coefficient of IMC layer and promotes its growth rate.The addition of MXene can increase the diffusion activation energy of IMC layer and then decrease the diffusion coefficient,thus prevent the growth of IMC.