Study Of The Electrochemical Migration Mechanism Of Pressureless Sintered Solder Paste

In recent years,power semiconductors have flourished.The third-generation semiconductors silicon carbide（Si C）and gallium nitride（Ga N）account for an increasing share of them year by year.Each generation of chips requires a new generation of packaging.Nano-Ag with its excellent electrical,thermal properties and its size effect resulting in low temperature sintering and high temperature service.These characteristics have led to the gradual replacement of traditional electronic packaging interconnects by nano-Ag as the common packaging interconnect material for third generation semiconductors.With the development of electronic devices towards miniaturisation and high density,the reduction of the interconnection size of electronic devices is inevitable and the failures caused by electrochemical migration of electronic devices are expected to become more serious.electrochemical migration has the potential to become a serious reliability issue in microelectronic devices.Also,Ag is poorly resistant to electrochemical migration.The study of the electrochemical mobility reliability of nano-Ag is therefore of great importance.This paper focuses on the preparation of pressureless sintered nano-Ag electrochemical migration specimens by printing nano-Ag slurry layers on Al₂O₃ ceramic substrates.The effects of changes in bias voltage,electrode spacing,sintering process parameters,Cl^-concentration and paste composition on the electrochemical migration behavior of Ag sintered layers were investigated.It was found that the increase in bias voltage and the decrease in electrode spacing lead to rapid failure of the specimen due to electrochemical migration,which occurs due to the increase in electric field force between the two electrodes.During the study of the sintering process parameters,it was found that the increase of the sintering temperature and the increase of the holding time lead to the formation of a dense mesh structure in the post-sintering tissue.It will prevent the anode dissolution in electrochemical migration.Ultimately,it has an inhibitory effect on electrochemical migration.Under different concentrations of Cl^-electrolyte solutions,it was found that low concentrations of Cl^-promoted the occurrence of electrochemical migration,medium concentrations had an inhibitory effect on electrochemical migration,and electrochemical migration behavior was completely inhibited at high concentrations.The increase in Cl^-concentration leads to the generation of large amounts of Ag Cl precipitates on the anode surface.The generation of Ag Cl inhibits the promotion of electrochemical migration by improved electrical conductivity,and Ag Cl prevents the contact between Ag and the electrolyte solution,reducing the anode dissolution rate.A comparison of the electrochemical migration behavior of Ag nanopaste and two Ag-Cu composite nanopastes revealed that the electrochemical migration failure time was prolonged with the addition of nano-Cu.In situ observation of the migration product growth process revealed that the migration product of pure Ag paste grows in the form of"cloud-like layer",while the addition of nano-Cu changes the growth pattern of the migration product.The migration product of composite paste shows single or multiple"dendritic"growth pattern.The microstructural analysis of the migration products showed that the morphology of the dendrites changed significantly from"elongated"to"wicker-like".Experimental investigations combined with mechanistic analysis were used to explain the difference in electrochemical migration behavior of interconnect layers between pure and composite Ag nano-pastes.During the electrochemical migration process,Cu will spill out of the sintered layer before Ag,preferentially forming hydroxide,which will later decompose into Cu O to adhere to the anode surface,thus preventing the occurrence of electrochemical migration.