Preparation And Microstructure And Property Optimization Of Cu/Invar Electronic Packaging Composites

Cu/Invar composite is recognized as one kind of new-style electronic packaging materials, because it combines the high electrical and thermal conductivity of copper and low expansion, high strength of Invar alloy. In this work, Cu/Invar composites were prepared through powder metallurgy, rolling and annealing. Effects of composition and rolling deformation on microstructures and properties of the composites were studied. In the Cu/Invar composites, Cu and Invar particles were coated by Ag in order to improve the sintering densification and restrain the Cu/Invar interface diffusion. Therefore, microstructures and properties of the composites were optimized. Finally, relationships between microstructures and properties of the composites were discussed.During the sintering process, the Invar alloy partly changes from the fee structure to the bec structure. After cold rolling and annealing, Ni atoms dissolve out of Cu and then diffuse into the Invar alloy, resulting in its structure transformation from bec into fee, again. Microstructure of the 40Cu/Invar composites changes from the discontinuous-distribution of Cu into the double-continuous-distribution of Cu and Invar, as increasing the rolling deformation. After rolling at a reduction of 70% and annealing at 750 癈, main properties of composites are:the relative density of 98.6%, the tensile strength of 360 MPa, the tensile elongation of 50%, the thermal conductivity of 29.3 W·(m·K)-1 and the CTE of 10.8x10-6 K-1, respectively.Cu/Ag(Invar) composites were fabricated by using Ag(Invar) composite powder, instead of the Invar alloy powder. In them, Ag is distributed among the Invar particles and at the Cu/Invar interface. On conditions of sintering at 750 ℃, rolling at a reduction of 55% and annealing at 450 ℃, main properties of the Cu/Ag(Invar) composites with 40 wt%(Cu+Ag) are:the relative density of 99%, the tensile strength of 853 MPa, the tensile elongation of 25%, the CTE of 11×10-6 K-1 and the thermal conductivity of 42.4 W·(m·K)-1, respectively. The thermal conductivity of the Cu/Ag(Invar) composites is much higher than that of the Cu/Invar composites.Ag(Cu)/Invar composites were prepared by using Ag(Cu) composite powder, instead of the Cu powder. On conditions of sintering at 800 ℃, rolling at a reduction of 65% and annealing at 450 ℃, Ag exists fibrously, and Cu and Invar are distributed continuously in the 40Ag(Cu)/Invar composites. Main properties of the composites are: the relative density of 99%, the tensile strength of 839 MPa, the tensile elongation of 25.5%, the CTE of 13.2×10-6 K-1 and the thermal conductivity of 53.2 W·(m·K)-1, respectively. The thermal conductivity of the Ag(Cu)/Invar composites is greater than that of the Cu/Ag(Invar) composites. This testing thermal conductivity is also consistent with the value calculated via the Maxwell model.