Study Of Interfacial Reaction And Properties Of The Interconnection Based On Ag@Sn Core-shell Particles

As electronic devices are developing toward miniaturization and multi-functionalization,heat generation is increasing drastically.Especially,some electronic devices used in oil drilling,aerospace,automobile,etc.are working in high-temperature environment.The demand for high-temperature solders is increasing every year,and yet the available solders all have their limitations.Through a structural adjustment on traditional TLP（Transient Liquid Phase）bonding,Ag@Sn core-shell structural TLP bonding enables the formation of a bondline for high-temperature service in a very short time,which is a promising new approach in the field of high-temperature packaging.However,the fabricating procedure of Ag@Sn powder is unstable.What’s more,there is still much room for improvement in the microstructure and properties of Ag@Sn interconnection.The purpose of this paper is to improve and perfect the Ag@Sn powder and the resulting interconnection through the adjustments in manufacturing technique and structure,and a further study on Ag/Sn and Cu/Sn/Ag interface.As the manufacturing technique of Ag@Sn powder is unstable,the Sn-plating technic on micron Ag particles was optimized.After an investigation in plating procedure,five factors were found as the most important ones that affect the stability and coating quality in plating,which are pretreatment of Ag particles,p H,agitator length,rotation rate and treatment after plating.After the thickness of Sn coating on Ag@Sn powder was reduced,voids were effectively eliminated.The theoretical service temperature,shear strength and electrical property were enhanced.The reflow time was reduced and the interconnection has higher impact resistance due to the formation ofζ-Ag at the interface.It was found thatζ-Ag won’t grow at the existence of Sn.It was discovered that the great amount of Sn could diffuse rapidly through the grain boundaries of Ag₃Sn,and therefore inhibit the growth ofζ-Ag.In order to investigate the adaptability of Ag@Sn preform in Cu-Cu interconnection,the microstructure evolution in Cu/Sn/Ag diffusion couple was studied.No defects were found between Cu-Sn IMCs（Intermetallics）and Ag-Sn IMCs,indicating that the Cu/Preform interface is not the weak point in a Ag@Sn interconnection.The reliability of Ag@Sn interconnection in the conditions of both long-term service and thermal shock was investigated.After aging test,the boundaries between particles became thicker and showed serration morphology.The main phases transformed from Ag/ζ-Ag to Ag/Ag（Sn）solid solution.Voids did not increase.The shear strength decreased slightly.However,the fracture surfaces showed more shear bands,indicating ductile fracture.After thermal shock test for 1500 cycles,only few samples failed.More failures were found in the samples with over-thick Sn layer at the Cu/preform interface.After extra tests on the thin-Sn-coating Ag@Sn interconnection,it was found that the reduction on the thickness of Sn coating could effectively prevent the formation of voids.At last,the fabrication of Ag@Sn solder paste was explored.It was found that the Ag@Sn solder paste that used flux cream as dispersant had the best weldability.Valid interconnection was achieved between Cu matrix and Ag@Sn solder paste.The average shear strength was 27.27 MPa.The fracture initiated at the interfaces between Ag@Sn solder paste and Cu matrix,and thereafter propagated through the interior of the joint.