Fabrication Of A Hybrid Paste Of Microscale Ag-plated Cu Flakes And Nanoscale Ag Particles And The Properties Of The Hybrid Paste Sintered Joints

With more and more applications of power semiconductor devices,the operation temperature may reach 250 to 300 °C,which requires that the interconnect materials between the semiconductors and substrates should be heat resistant.Under the circumstance,the silver paste has been considered as one of the most promising interconnect materials.Further,it is feasible to use the hybrid silver paste,in which the microscale Ag flakes tend to form a lamination network and the nanoscale Ag particles can fill gaps.It has been shown that hybrid silver paste sintered joints are much denser than nano-silver paste sintered ones due to the intensive shrinkage and limited volatilization in the nano-silver paste during sintering.However,the high cost of the nanoscale Ag particles has limited its wide application.Aiming at reducing the cost of silve paste used for electronic packaging,in this thesis work,a systematical study on pretreatment of the micro-Ag flakes,volatile solvents and binder,synthesis of nano-Ag particles with controllable size,and the influence of the nano-Ag particle size,morphology of micro-Ag flakes and dispersion mode of nano-Ag particles on the properties of hybrid silver paste sintered joints were conducted.Then,microscale Ag-plated Cu flakes with high covering degree were prepared and used to replace micro-Ag flakes in the hybrid paste.Finally,a hybrid paste consisting of microscale Ag-plated Cu flakes,nano-Ag particles and volatile solvents has been prepared.Results show that organic acid pretreatment of micro-Ag flakes,selection of suitable volatile solvents,binder and other additives may promote uniform mixture and distribution of the micro-Ag flakes and water based nano-Ag particles,leading to increase of properties of hybrid silver paste sintered joints.The nano-Ag particle size increases with decreasing reagent PH value,which makes the synthesis of nano-Ag particles with controllable size.The sintered joints by using the hybrid silver paste of 12 nm nano-Ag particles and micro-Ag flakes with a mixture ratio of 3:2 show the average shear strength of 19.2 MPa and average electrical resistance of 0.009 m?·cm.After sensibilization treatment and increasing Ag-plating time,Ag-plated Cu fleakes were prepared with the covering degree of almost 100%.Further,after ball-milling,Ag-plated Cu flakes become finer and the plating structure is more likely to be densified.The average shear strength of sintered joints using the hybrid paste with Ag-plated Cu flakes is up to 13.6 MPa and the average electrical resistance is 0.024 m?·cm.