Study Of Micron Silver/Copper Particles Reinforced Tin-based Solder

With the continuous development of electronic technology,new electronic devices have higher requirements for miniaturization and integration.In order to meet the above requirements for high-performance electronic devices,the development and design of appropriate three-dimensional packaging structures have become an important part of electronic packaging research.The realization of three-dimensional packaging inevitably requires a multi-level packaging process.Traditionally multilevel packaging process relies on the sequential use of solders with different melting points,which brings great process complexity and extremely high production cost,limiting the application potential of three-dimensional packaging.In order to solve these problems,this article believes that the development of new types of connection materials is imperative.The processing temperature of this new connection material can be increased after a connection process,thereby obtaining stability in the subsequent connection process,making it possible to use the same material and the same process for multi-level packaging.There are sevaral candidates,such as nano solder paste sintering process,solid-liquid interdiffusion bonding process and composite solder brazing process.Among these,the tin-based composite solder reinforced with micrometer metal particles has the advantages of low cost,simple process,flexible and changeable component,etc.So that,its application prospect is the most extensive.Therefore,this work will use chemical reduction to prepare micron silver and micron copper particles of different shapes and sizes,using to prepare tin-based composite solders,exploring the application prospects of silver/copper particle-reinforced tin-based composite solders in multi-level packaging..Firstly,by adjusting the metal salt,reducing agent,dispersant,reaction temperature and other parameters of the chemical reduction method,three kinds of micron particles were successfully prepared,which were micron silver flakes with an average diameter of 2 microns and spherical micron silver and micron copper with an average diameter of 1 micron.Above three micron particles and the 200 mesh copper powder purchased from the market were used as the reinforcing phase to prepare tinbased composite solder.By the comparison among them,the qualitative influnence of the type,shape and size of the reinforcing phase particles to composite solder came out.Subsequently,the melting temperature,microstructure and mechanical properties of the composite solder were tested.Analysis of the phase diagram of the tin-silver-copper system shows that the content of copper can greatly increase the melting-end temperature(liquid line temperature)of the solder system.DSC test shows that the copper particles in the composite solder can be affected by reflow treatment.With 10 wt.% of micron copper added,the melting-end temperature of the solder can be increased by 13°C.Microstructure analysis and shear tests show that with a short time of melting,particles of larger size(70 microns)cannot fully react with the solder,remaining certain amount of metal,which will bring hidden danger about stability to the device.As aspect of smaller size(1-2 microns),both silver and copper particles can fully react with tin-based solder,producing a fine intermetallic compound structure,which greatly enhances its fracture strength and the fracture modle of solder transform from tenacity to brittle.In addition,this paper also analyzes the theoretical calculation of the reaction thermodynamics of copper-tin system and the mathematical modeling of the reaction kinetics under quasi-equilibrium and non-equilibrium conditions.Thermodynamic calculation results show that copper and tin react preferentially to form Cu6Sn5 compounds near the melting point of tin.Growth kinetics under quasi-equilibrium conditions shows that if the growth process of Cu6Sn5 is controlled by diffusion,its growth will become extremely slow,which explains the problem of metal residue of large-size copper particles.Mathematical modeling of non-equilibrium kinetics shows that the optimal content of copper particles in the composite solder is about 12.5% by volume,and the size of copper particles has no effect on the shape of its microstructure,but smaller particles can form a finer structure.