Research On Silver-Indium TLP Solder Preparation For Low-temp Refolwing And High-temp Service

With the wide use of electronic devices in the more complex service environment,high-temperature,high-frequency as well as power chips with capability of serving under extreme conditions become more and more important.It has brought a great challenge for solder to serve with long-term reliability under high temperature.Besides,the heat generated by the chip itself becomes much higher with the increase of interconnect density and power density,which makes it necessary to search for the die-attach material with a higher reliability at elevated temperatures.On the other hand,to adapt to actual process and minimize thermal stress,the bonding temperature and pressure should not be too high.So far,methods such as nano-silver paste sintering,solid liquid inter diffusion bonding(SLID),transient liquid phase sintering(TLPS),and nanoporous bonding(NPB)etc.have been developed for low-temperature joining and high-temperature serving applications.While each method has its drawback.the purpose of this study is to explore the new Ag-In solder materials which can achieve connection rapidly under low temperature while enable operation at extremely high temperatures.In this paper,the solder of Ag@In core-hell particles preform was fabricated.Under reflowing temperature of 200 ?,the outer In layer will melt and react with the inner core.The Ag-In intermetallics(IMCs)will form during the reaction.he solder joint with Ag particles dispersing in IMCs has higher temperature(>660 ?),which could be operated in high temperature.The core-shell particles were prepared by electroless plating,different solutions were used to plate spherical Ag particles with the diameters of 3?m and 30?m,and the effects of In3+ concentration and plating times on the thickness of In coating were studied.A novel Ag-In bonding material was explored.The material was fabricated by In paste and foam Ag.Indium paste was printed on foam Ag with pore size of 20 ?m by screen printing,and the pores were filled with molten In by capillary force in a subsequent reflow process.Two novel attach materials were prepared for TLP bonding,both of which meet the requirements as mentioned above.Ag@In core-shell particles were pressed to preform then reflowed,the joint exhibited higher quality with thicker In shell.However,cracks and viods were inevitably observed due to the limitations of electroless plating process and the characteristics of the spherical structure.By using foam Ag with In fill as thebonding material,an expected result was achieved as the joint consisted of Ag framework and IMC compounds.