Studies On The Preparation Of Cu/Invar Electronic Packaging Composites By Powder Metallurgy

With the advent of the information age, rapid development of electronic industryrequires high integration scale, miniaturization and refinement of the electronicdevices. Correspondingly, it makes higher and higher demands on electronicpackaging materials, promoting research and the development of new packagingmaterials in the world. Cu/Invar composite was designed to combine excellentelectrical and thermal conductivity of Cu and low coefficient of thermal expansion ofInvar alloys. The composites are of course predicted to possess excellent formabilityand weldability, and they are also electroplateable, compared with somecurrently-used electronic packaging materials such as Al/SiCp, W/Cu, and Kovar. Thecomposites have potential to be ideal alternative materials of them in future.Invar alloy nanocrystalline powder was firstly prepared by mechanical alloying.Microstructures, morphologies and composition homogenizations of the Invar alloypowders were investigated, and the alloying mechanism of the powder was alsodiscussed. The Cu/Invar composites were fabricated by powder-metallurgy. Anorthogonal experiment scheme was designed to produce the composites,microstructures, mechanical and physical properties of the composites were analyzedto optimize the process parameters of the composites.In the initial milling stage (5-10h), the Invar alloy particles are flat lamellarcomposites due to micro-forging and cold-welding of the alloy powder. Ni atoms ofthe FeNi50alloy particles diffuse into the FeNi30alloy ones to accelerate thecomposition homogenization of the Invar alloy powder. After the powder milled for40h, a homogeneous α’-Fe (Ni) solid solution completely forms. The mechanicallyalloyed Invar alloy powder composes of the spherical and smooth particles of anaverage grain size of about12nm. As the milling time increased, some big alloyparticles break into the finer Invar alloy ones.Distributions of Cu and Invar in the Cu/Invar composites are both uniform. Acontinuous Cu net forms in the composites having the Cu content of40wt%andabove, however, it is replaced by a continuous Invar net when the Cu content in thecomposites is30wt%and below. The densities of the composites increase as theforming pressure and sintering temperature increased. However, the high sinteringtemperature results in the serious atom diffusion in the composites, leading to thereduction of the electrical conductivities and thermal conductivities of the composites, and the increase of the coefficient of thermal expansion of the composites. Taking thedensity and hardness of composite as index, the optimal process parameters are:forming pressure of600MPa, sintering temperature of1150℃, holding time of90min and Cu content of50wt%. Taking the electrical resistivity as index, the optimalprocess parameters are: forming pressure of600MPa, sintering temperature of1000℃,holding time of60min and Cu content of50wt%. The measured thermalconductivities of the sintered composites are consistent with the calculated results viathe Wiedemann-Franz law. Due to the atom interdiffusion during sintering and theexsistences of the pores and interfaces in the composites, the electrical resistivities ofthe composites predicted via the Russell, son Frey or Bruggeman model isconsistently smaller than the tested values.