Research On Low-temperature Sintered Copper Interconnection Method And Ratcheting Fatigue Behavior

Recently,the high temperature resistance,high output power,and high breakdown voltage of the third generation semiconductor materials make it possible for electronic components to work at high temperature above 250℃in the field of new energy vehicles,aircraft,aerospace,etc.However,the traditional packaging and interconnection materials can not achieve the stable operation of electronic components at high temperature.As a new type of packaging and interconnection materials,sintered silver has attracted extensive attention due to its high melting point,high thermal conductivity and high conductivity.However,the high cost of silver and susceptibility to electromigration limit its wide application in power electronics.Copper has the advantages of low cost,high conductivity and strong resistance to ion migration,which is considered as a substitute packaging interconnection material for silver.However,the current research mainly focuses on the improvement of copper sintering process,and there are few researches on the ratchet deformation fatigue failure of sintered copper joints.Therefore,the sintering process of low-temperature sintered copper joints is discussed in detail,and the ratcheting behavior of sintered copper joints at room temperature is investigated by the non-contact measurement method.Firstly,this paper explores the sintering process of low-temperature sintered copper joints and discusses the effects of sintering temperature,sintering assistant pressure and sintering holding time on the low-temperature sintered copper joints.The results show that the performance of sintered copper joints are improved and tend to be stable with the increase of sintering temperature,assistant pressure and holding time.The optimal sintering conditions are sintered at 270 ^oC for 30 min,under 5 MPa in forming gas（4%H₂/N₂）.Under this conditions,the shear strength and resistivity of the sintered copper joints are 42.2 MPa and 10.5×10^-8?·m,respectively.Besides,the sintered copper joints are not oxidized.In addition,no oxidation is occurs in the sintered copper joints.The microstructure of the sintered copper joints is compact with a porosity of 13.3%.Secondly,the effects of stress rate,mean stress,stress amplitude,stress ratio and maximum stress on ratcheting behavior and fatigue life of the sintered copper joints were studied by non-contact measurement.All experiments were conducted under the stress-controlled cyclic loading at room temperature.The results show that the uniaxial shear behavior of the sintered copper joints is rate dependent.The shear strength of the sintered copper joints decreases with the decrease of the stress rate,but the shear strain increases;the ratchet strain of the sintered copper joints decreases with the decrease of the average stress and the stress amplitude,but increases with the decrease of the stress ratio and the stress rate.At the same time,the ratchet strain of the sintered copper joints increases with the decrease of the mean stress and the stress amplitude.Besides,stress amplitude or average stress will reduce the fatigue life of the sintered copper joints,while the ratchet fatigue life of the sintered copper joints increases with the increase of stress ratio and stress rate.At higher stress levels,the failure of sintered copper joints was mainly attributed to ratcheting damage,and the failure of sintered copper joints under a low stress could be attributed to fatigue damage failure.In addition,three fatigue life prediction models that taking mean stress into consideration,such as modified Goodman model,Gerber model and SWT model,are used to predict the fatigue life of sintered copper joints.The results show that the modified Goodman model can better predict the fatigue life of sintered copper joints at room temperature.