Preparation Of Cu-Ag Bimetallic Core-shell Nanoparticles For Packaging

"Moore’s Law",Limited by the fact that transistor circuits are gradually approaching their performance limits,begun to slow down.In order to continue to develop "Moore’s Law",people turn their attention to packaging which is the last key process in electronic products.Packaging,providing electrical paths,thermal paths and effective protection for chips,has a huge impact to the cost,size and performance of the product.The increasing of the density of the packaging contributes greatly to the strength of the interconnection for electronic products.Therefore,the development of new packaging materials and packaging structures has great research significance.Cu-Ag core-shell nanoparticles(Cu@Ag NPs)are highly anticipated bimetallic materials with wide electronic applications.However,it is still crucially challenging to obtain well-covered Ag shells and facilitate the synthetic process,and the sintering and migration behaviors of Cu@Ag NPs are also poorly understood.In this study,we developed a facile method for synthesizing Cu@Ag NPs.With the addition of L-Histidine during synthesis,the Cu@Ag NPs could obtain attractive characteristics including low Ag content(10.1 at.%),compact and uniform Ag shells(～5% thickness relative to the particle diameter),good dispersibility,and satisfactory sphericity.At an optimum element ratio of Cu:Ag = 10:1,the Cu@Ag NPs could form compact and thin Ag shells,and thus had desirable comprehensive performance of high oxidation resistance(no oxides after air exposure for three months),reliable sintering property(60 MPa shear strength under the sintering temperature of 300℃).The results indicated that the complexing effect of L-Histidine significantly improved the coating quality of Ag shells and that the Cu-Ag core-shell structure could promote the coalescence of the nanoparticles and is conducive to the electrochemical migration resistance.Our study develops an applicable method for the synthesis of Cu@Ag NPs,and provides helpful experimental basis for understanding their sintering behaviors.The comprehensive performance of Cu@Ag NPs makes them a promising interconnect material in future electronic industry.