Microstructure And Properties Of Al-50Si-0.5X (X=Sc,La,Nb) Alloy For Electronic Packaging

Al-50Si alloy is an ideal material for electronic packaging because of its high thermal conductivity,low coefficient of thermal expansion（CTE）,low density,good surface coating and laser welding.The electronic packaging materials with high strength play a good mechanical support role for electronic components,thus ensuring their service reliability.In this paper,the microstructure characteristic and its evolution after heating of rapidly solidified Al-50Si-0.5X（X=Sc,La,Nb）alloys were analyzed,which could provide reference for subsequent hot-pressing parameters.The effects of microalloying elements on the microstructure,mechanical properties and thermophysical properties of hot-pressed alloys were compared,and the strengthening mechanisms of the alloys were discussed.The main results are as follows:（1）The Si phase in the microstructure of the alloy ribbons with a thickness of 50-150μm presents as fine particles,and the Si particle size in the 50μm thin ribbon is the smallest of only 0.53-0.72μm.The microalloying elements are supersaturated in the Al matrix.（2）After heating at 500 and 530℃ for 1 h,the eutectic Si phase is dissolved,the supersaturated Si atoms are precipitated.The precipitated Si phase agglomerates with the primary Si phase,resulting in the coarsening of the Si phase.After holding at 560℃ for 1 h,the Si phase is connected into a network,and the precipitates is homogeneously distributed in the Al matrix.After holding at 600℃ for 1 h,the Si phase further coarsens to form a closedα-Al phase.The size of precipitates increased to 572.2-960.6 nm.The microstructural observations of the alloy ribbons held at 560℃ for 0.5,1,2 and 3 h show that the Si phase is significantly coarsened after holding for 2 h,and a closed Al phase begins to appear.（3）The addition of microalloying elements Sc,La and Nb has little effect on the size,distribution and morphology of the Si phase in the Al-50Si alloy.The precipitates in the three alloys are Al Si₂Sc₂phase（V phase）,Al₂Si₂La phase and Nb Si₂phase,respectively.The size of the precipitates is concentrated in 400-600 nm,with an average size of approximately 550.0 nm.The volume fractions of the precipitates are2.5%,3.0%and 3.6%,respectively.（4）Precipitation strengthening is the main strengthening mechanism of the alloys.The size of the three precipitates is similar,and the Nb Si₂phase has the highest volume fraction of 3.6%.It shows that the Al-50Si-0.5Nb alloy has the highest tensile strength of 254.0 MPa,followed by the Al-50Si-0.5La alloy with a tensile strength of 244.0 MPa,and the Al-50Si-0.5Sc alloy has the lowest strength of 234.0 MPa.However,Al-50Si-0.5Nb alloy has the lowest fracture and impact toughness.Compared with the Al-50Si alloy,the formation of the precipitates increases the interfacial area and hinders the conduction of phonons and electrons,leading to a reduction in thermal conductivity of1.7%,2.6%and 2.9%of Al-50Si-0.5X（X=Sc,La,Nb）alloys after microalloying,respectively.In addition,the precipitates and the Si phase suppress the thermal expansion of the Al matrix,and the CTE of the alloys after microalloying decreases slightly.52 figures,7 tables and 101 references...