Study On Liquid-solid Electromigration Behavior And Mechanism Of Sn-3.0Ag-0.5Cu Lead-free Solder Bumps In High Power Devices

With the demands of continuous miniaturization,high-performance and lead-free in microelectronics industry,the diameter of solder bumps is downsizing continuously and the current density through each solder bump increases sharply,causing electromigration(EM)to become a serious reliability issue.Miniaturization make grid size continues to decrease,increasing packaging density and power density,the current density passing through the solder joints becomes larger.In the present work,synchrotron radiation real-time imaging technology was used to in situ observe the liquid-solid electromigration(L-S EM)behavior of the Cu/Sn-3.0Ag-0.5Cu(SAC305)/Cu interconnect and the dissolving rate of the cathode Cu was calculated;the effect of temperature and current density on the Cu-Ni interaction were investigated of Cu/SAC305/Ni interconnects;Cu/SAC305/Cu(Ni)flip chip solder joints were used to further investigate the L-S EM behavior.The main conclusions are drawn as follows:(1)For the L-S EM of Cu/SAC305/Cu line-type interconnect,the dissolving rate of the cathode Cu is accelerated and tiny Cu6Sn5 intermetallic compounds(IMCs)and irregular-shaped IMCs were generated at the cathode and anode side,respectively.The IMCs at the anode side were thicker than those at the cathode side.The dissolving thickness of the cathode Cu can reach 5.33 ?m after 1 h L-S EM under the current density of 80 A/cm2 at 240 oC and a calculated method for the dissolution thickness of cathode Cu was established which can better predict the dissolution thickness of cathode Cu in the process of L-S EM.(2)For the L-S EM of Cu/SAC305/Ni line-type interconnect,(Cu,Ni)6Sn5 IMC were generated at the both side and Ni content was becoming higher with the location approaching the Ni side.J chem Cu was greater than J em Cu when the Cu/SAC305/Ni interconnect was under lower current density,showing the IMCs on the cathode side was thicker than those on the anode side;J chem Cu was less than J em Cu when the Cu/SAC305/Ni interconnect was under higher current density,showing the IMCs on the cathode side was thinnerr than those on the anode side.(3)For the L-S EM of Cu/SAC305/Cu flip chip soldr joint,the Cu lead of cathode side almost dissolved;the irregular-shaped Cu6Sn5 IMCs were formed at the anode side and in the solder joint;L-S EM caused a polarity effect,i.e.,the IMCs at the anode side were thicker than those at the cathode side.For the L-S EM of Cu/SAC305/Ni flip chip soldr joint,the cathode Ni UBM dissolved heavily and very thick(Cu0.80Ni0.20)6Sn5 IMCs layer was generated on the cathode side(7.73 ?m);the anode Cu substrate was almost consumed and irregular-shaped(Cu0.89Ni0.11)6Sn5 IMCs layer was formed at the anode side;the irregular-shaped IMCs were also formed in the solder joint.