Preparation And Interface Optimization Of Cu/Ag(Invar) Electronic Packaging Composites

With the progresses of the times,developments of the electronic industry and diversification of the electronic products put forward higher and higher requirement on the electronic packaging technologies and materials.The new electronic packaging composites of high thermal conductivity（TC）and low coefficient of thermal expansion（CTE）are paid more sustained attention.The newly-developed Cu/Invar composites have a typical disadvantage,i.e.the atom interdiffusion occurred in the sintering process of the composites results in the change of the compositions of Cu and Invar,which have very worse effects on the properties of the composites.Therefore,exploration of the methods which can effectively prohibit the Cu/Invar interfacial diffusion and then improve the properties of the composites is the key on developing the Cu/Invar composites.In this study,an electroless plating technique was employed to form the continuous Ag layer on the Invar alloy powder.The influences of the pH value of the plating solution and plating time on the electroless Ag plating process and the morphologies and interfacial structures of the Ag（Invar）composite powder were studied.And thus,the Ag（Invar）composite powder and the Cu powder were used as raw materials to fabricate the Cu/Ag（Invar）composites via powder metallurgy and thermal-mechanical treatment.The microstructures and properties of the composites were thoroughly researched.The Ag（Invar）composite powder was produced by electronic plating the Ag layer on the Invar powder,using the silver-ammonia solution as the plating solution and the potassium sodium tartrate solution as reducing agent.On the conditions of that the pH value of the plating solution is 11.5 and the plating time is 30 min,the Ag layer on the Ag（Invar）powder is about 2-3 μm in thickness,which is continuous and dense with a smooth and even morphology and contacts tightly with the Invar substrate.Ag in the Cu/Ag（Invar）composites formed via pressureless sintering mainly distributes at the Cu/Invar interface,the others in the Invar grains and in the Cu matrix.The Ag particles in the Cu matrix are in a short-rod shape.The 40Cu/Ag（Invar）composites sintered at 775 have the density of 8℃ 6.71%,the hardness of HV 140.5,the TC of 41.63 W·（m·K）^-1 and the CTE of 10.68×10^-6 K^-1.These properties are superior to those of the sintered 40Cu/Invar composites and the 40Cu/Ag（Invar）composites using the ball-milling enwrapped Ag（Invar）composite powder as raw material.After the thermal-mechanical treatment of cold-rolling of 55% reduction and final annealing at 400℃,the Cu/Ag（Invar）composites is nearly fully dense.The Cu and Invar components in the composites are distributed as a bi-continuous network structure.Ag mostly enwraps the Invar particles.The 40Cu/Ag（Invar）composites are anisotropy after the thermal-mechanical treatment,which have the density of 98.0%,the hardness of HV 256.The composites have the TC of 53.68 W·（m·K）^-1,the CTE of 11.24×10^-6 K^-1 along the deformation orientation.The comprehensive properties of the composites highly exceed those of the 40Cu/Invar composites and the 40Cu/Ag（Invar）composites using the ball-milling enwrapped Ag（Invar）composite powder as raw material after the thermal-mechanical treatment.